START-INFO-DIR-ENTRY * mysql: (mysql). *MySQL* documentation. END-INFO-DIR-ENTRY This is a manual for *MySQL*. This version is about the 3.22.14-gamma version of *MySQL*. For a *3.20* version see the relevant distribution. General Information about *MySQL* ********************************* This is the *MySQL* reference manual; it documents *MySQL* version 3.22.14-gamma. *MySQL* is a very fast, multi-threaded, multi-user and robust SQL database server. For Unix/OS2 platforms *MySQL* is basically free, for Microsoft platforms you must get a *MySQL* license after a trial time of 30 days. *Note Licensing and Support::. The *MySQL* home page (http://www.tcx.se/) provides the latest information about *MySQL*. For a discussion of *MySQL*'s capabilities, see *Note Features::. For installation instructions, see *Note Installing::. For tips on porting *MySQL* to new machines or operating systems, see *Note Porting::. *Note Upgrading-from-3.21::, for information about upgrading from a 3.21 release. For examples of SQL and benchmarking information, see the `bench' directory. For a history of new features and bug fixes, see *Note News::. For a list of currently known bugs and misfeatures, see *Note Bugs::. For future plans, see *Note TODO::. For a list of all the contributors to this product, see *Note Credits::. *IMPORTANT:* Send bug (error) reports, questions and comments to the mailing list at . *Note Bug reports:: For source distributions, the `mysqlbug' script can be found in the `scripts' directory. For binary distributions, `mysqlbug' can be found in the `bin' directory. If you have any suggestions concerning additions or corrections to this manual, please send them to the *MySQL* mailing list () with the following subject line: `documentation suggestion: [Insert Topic Here]'. *Note Mailing-list::. What is *MySQL*? ================ *MySQL* is a true multi-user, multi-threaded SQL (Structured Query Language) database server. SQL is the most popular database language in the world. *MySQL* is a client/server implementation that consists of a server daemon `mysqld' and many different client programs and libraries. The main goals of *MySQL* are speed, robustness and ease of use. *MySQL* was originally developed because we at TcX needed a SQL server that could handle very large databases an order of magnitude faster than what any database vendor could offer to us. We have now been using *MySQL* since 1996 in an environment with more than 40 databases containing 10,000 tables, of which more than 500 have more than 7 million rows. This is about 100 gigabytes of mission-critical data. The base upon which *MySQL* is built is a set of routines that have been used in a highly demanding production environment for many years. While *MySQL* is still in development, it already offers a rich and highly useful function set. The official way to pronounce *MySQL* is "My Ess Que Ell" (Not MY-SEQUEL). About this manual ================= This manual is currently available in TeXInfo, plain text, Info and HTML versions. Because of their size, PostScript and PDF versions are available for separate download. The primary document is the TeXInfo file. The HTML version is produced automatically with a modified version of `texi2html'. The plain text and Info versions are produced with `makeinfo'. The Postscript version is produced using `texi2dvi' and `dvips'. The PDF version is produced with the Ghostscript utility `ps2pdf'. This manual is written and maintained by David Axmark, Michael (Monty) Widenius, Paul DuBois and Kim Aldale. For other contributors, see *Note Credits::. Conventions used in this manual ------------------------------- This manual uses certain typographical conventions: `constant' Constant-width font is used for command names and options; SQL statements; database, table and column names; C and Perl code; and environment variables. Example: "to see how `mysqladmin' works, invoke it with the `--help' option." `filename' Constant-width font with surrounding quotes is used for filenames and pathnames. Example: "the distribution might be installed under the `/usr/local/' directory." `c' Constant-width font with surrounding quotes is also used to indicate character sequences. Example: "to specify a wildcard, use the `%' character." *italic* Italic font is used for emphasis, *like this*. *boldface* Boldface font is used for access privilege names (e.g., "do not grant the *process* privilege lightly") and occasionally to convey *especially strong emphasis*. When commands are shown that are meant to be executed by a particular program, the prompt for the command indicates the program. For example, `shell>' indicates a command that you execute from your login shell, and `mysql>' indicates a command that you execute from the `mysql' client: shell> type a shell command here mysql> type a mysql command here Shell commands are given using Bourne shell syntax. If you are using a `csh'-style shell, you may need to issue commands slightly differently. For example, the sequence to set an environment variable and run a command looks like this in Bourne shell syntax: shell> VARNAME=value some_command For `csh', you would execute the sequence like this: shell> setenv VARNAME value shell> some_command Database, table and column names often must be substituted into commands. To indicate that such substitution is necessary, this manual uses `db_name', `tbl_name' and `col_name'. For example, if you see this: mysql> SELECT col_name FROM db_name.tbl_name; It means that were you to enter a similar statement, you would supply your own database, table and column names, perhaps like this: mysql> SELECT author_name FROM biblio_db.author_list; SQL statements may be entered in uppercase or lowercase. When this manual shows a SQL statement, uppercase is used for particular keywords if those keywords are under discussion (to emphasize them) and lowercase for the rest of the statement. So you might see the following in a discussion of the `SELECT' statement: mysql> SELECT count(*) FROM tbl_name; On the other hand, in a discussion of the `COUNT()' function, the statement would be written like this: mysql> select COUNT(*) from tbl_name; If no particular emphasis is intended, all keywords are written in uppercase. In syntax descriptions, square brackets (`[' and `]') are used to indicate optional words or clauses: DROP TABLE [IF EXISTS] tbl_name When a syntax element consists of a number of alternatives, the alternatives are separated by vertical bars (`|'). When one member from a set of choices may be chosen, the alternatives are listed within square brackets. When one member from a set of choices must be chosen, the alternatives are listed within braces (`{' and `}'): TRIM([[BOTH | LEADING | TRAILING] [remstr] FROM] str) {DESCRIBE | DESC} tbl_name {col_name | wild} History of *MySQL* ================== We once started off with the intention to use `mSQL' to connect to our own fast low-level (ISAM) tables. However, after some testing we came to the conclusion that `mSQL' was not fast enough or flexible enough for our needs. This resulted in a new SQL interface to our database but with almost the same API interface as `mSQL'. This API was chosen to ease porting of third-party code. The derivation of the name *MySQL* is not perfectly clear. Our base directory and a large number of our libraries and tools have had the prefix "my" for well over 10 years. However, Monty's daughter (some years younger) is also named My. So which of the two gave its name to *MySQL* is still a mystery, even for us. The main features of *MySQL* ============================ * Fully multi-threaded using kernel threads. That means it easily can use multiple CPUs if available. * C, C++, Java, Perl, Python and TCL API's. *Note Clients::. * Works on many different platforms. *Note Which OS::. * Many column types: signed/unsigned integers 1, 2, 3, 4 and 8 bytes long, `FLOAT', `DOUBLE', `CHAR', `VARCHAR', `TEXT', `BLOB', `DATE', `DATETIME', `TIMESTAMP', `YEAR', `SET' and `ENUM' types. *Note Column types::. * Very fast joins using an optimized one-sweep multi-join. * Full operator and function support in the `SELECT' and `WHERE' parts of queries. Example: mysql> SELECT CONCAT (first_name, " ", last_name) from tbl_name WHERE income/dependents > 10000 AND age > 30; * SQL functions are implemented through a highly-optimized class library and should be as fast as they can get! Usually there shouldn't be any memory allocation at all after the query initialization. * Full support for SQL `GROUP BY' and `ORDER BY' clauses. Support for group functions (`COUNT()', `AVG()', `STD()', `SUM()', `MAX()' and `MIN()'). * Support for `LEFT OUTER JOIN' with ANSI SQL and ODBC syntax. * You can mix tables from different databases in the same query (as of version 3.22). * A privilege and password system which is very flexible and secure, and which allows host-based verification. Passwords are secure since all password traffic when connecting to a server is encrypted. * ODBC (Open-DataBase-Connectivity) for Windows95 (with source). All ODBC 2.5 functions and many others. You can, for example, use Access to connect to your *MySQL* server. *Note ODBC::. * Very fast B-tree disk tables with index compression. * 16 indexes per table are allowed. Each index may consist of 1 to 15 columns or parts of columns. The maximum index length is 256 bytes (this may be changed when compiling *MySQL*). An index may use a prefix of a `CHAR' or `VARCHAR' field. * Fixed-length and variable-length records. * In-memory hash tables which are used as temporary tables. * Handles large databases. We are using *MySQL* with some databases that contain 50,000,000 records. * All columns have default values; you can use `INSERT' to insert a subset of a table's columns and columns that were not explicitly given values will be set to their default values. * Uses GNU Automake, Autoconf, and `libtool' for portability. * Written in C and C++. Tested with a broad range of different compilers. * A very fast thread-based memory allocation system. * No memory leaks. Tested with a commercial memory leakage detector (`purify'). * Includes `isamchk', a very fast table check, optimize and repair utility. *Note Maintenance::. * All data are saved in ISO-8859-1 Latin1 format. All comparisons for normal string columns are case insensitive. * Full support for the ISO-8859-1 Latin1 character set. For example, the Scandinavian characters *a, "a and "o are allowed in table and column names. * Sorts according to the ISO-8859-1 Latin1 character set (the Swedish way at the moment). It is possible to change this in the source by adding new sort order arrays. To see an example of very advanced sorting, look at the Czech sorting code. *MySQL* supports many different character sets that can be specified at compile time. * Aliases on tables and columns as in the SQL92 standard. * `DELETE', `INSERT', `REPLACE', and `UPDATE' return how many rows were affected. * Function names do not clash with table or column names. For example, `ABS' is a valid column name. The only restriction is that for a function call, no spaces are allowed between the function name and the `(' that follows it. *Note Reserved words::. * All *MySQL* programs can be invoked with the `--help' or `-?' options to obtain online assistance. * The server can provide error messages to clients in many languages. *Note Languages::. * Clients connect to the *MySQL* server using a TCP/IP connection or Unix socket. * The *MySQL*-specific `SHOW' command can be used to retrieve information about databases, tables and indexes. The `EXPLAIN' command can be used to check how the optimizer resolves a query. How stable is *MySQL*? ====================== This section addresses the questions, "how stable is *MySQL*?" and, "can I depend on *MySQL* in this project?" At TcX, *MySQL* has worked without any problems in our projects since mid-1996. When *MySQL* was released to a wider public, we noticed that there were some pieces of "untested code" that were quickly found by the new users who made queries in a different manner. Each new release has had fewer portability problems than the previous one, even though each has had many new features, and we hope that it will be possible to label one of the next releases "stable". Each release of *MySQL* has been usable and there have been problems only when users start to use code from "the gray zones". Naturally, outside users can't know what the gray zones are; this section attempts to indicate those that are currently known. Here we will try to clarify some issues and to answer some of the more important questions that seem to concern many people. This section has been put together from information gathered from the mailing list (which is very active in reporting bugs). The descriptions deal with the 3.21.x version of *MySQL*. All known and reported bugs are fixed in the latest version, with the exception of the bugs listed in the BUGS file which are things that are "design"-related. *MySQL* is written in multiple layers and different independent modules. Here is a list of the different modules and how well-tested each of them is: *The ISAM table handler -- Stable* This is how all the data are stored. In all *MySQL* releases there hasn't been a single (reported) bug in this code. The only known way to get a corrupted table is to kill the server in the middle of an update. Even that is unlikely to destroy any data beyond rescue, because all data are flushed to disk between each query. There hasn't been a single bug report about lost data because of bugs in *MySQL*, either. *The parser and lexical analyser -- Stable* There hasn't been a single reported bug in this system for a long time. *The C client code -- Stable* No known problems. In early 3.20 releases, there were some limitations in the send/receive buffer size. In 3.21.x, the send/receive buffer is now dynamic up to a default of 512K. *`mysql', `mysqladmin' and `mysqlshow', `mysqldump',* and `mysqlimport' -- Stable *Basic SQL -- Stable* The basic SQL function system and string classes and dynamic memory handling. Not a single reported bug on this system. *Query optimizer -- Gamma* *Range optimizer -- Stable* *Join optimizer -- Stable* *Locking -- Gamma* This is very system-dependent. On some systems there are big problems using standard OS locking (`fcntl()'). In these cases, you should run the *MySQL* daemon with the `--skip-locking' flag. Problems are known to occur on some Linux systems and on SunOS when using NFS-mounted file systems. *Linux threads -- Gamma* The only problem found has been with the `fcntl()' call, which is fixed by using the `--skip-locking' option to `mysqld'. Some people have reported lockup problems with the 0.5 release. *Solaris 2.5+ pthreads -- Stable* We use this for all our production work. *MIT-pthreads (Other systems) -- Gamma* There have been no reported bugs since 3.20.15 and no known bugs since 3.20.16. On some systems, there is a "misfeature" where some operations are quite slow (a 1/20 second sleep is done between each query). Of course, MIT-pthreads may slow down everything a bit, but index-based `SELECT' statements are usually done in one time frame so there shouldn't be a mutex locking/thread juggling. *Other thread implementions -- Alpha - Beta* The ports to other systems are still very new and may have bugs, possibly in *MySQL*, but most often in the thread implementation itself. *`LOAD DATA ...', `INSERT ... SELECT' -- Stable* Some people have thought they have found bugs here, but these have turned out to be misunderstandings. So check the manual before reporting bugs! *`ALTER TABLE' -- Gamma* Small changes in 3.22.12 *DBD -- Gamma* Now maintained by Jochen Wiedmann . Thanks! *`mysqlaccess' -- Gamma* Written and maintained by Yves Carlier . Thanks! *`GRANT' - Alpha* Big changes done in *MySQL* 3.22.12. **MyODBC* (uses ODBC SDK 2.5) -- Beta* It seems to work well with some programs. TcX provides email support for paying customers, but the *MySQL* mailing list usually provides answers to common questions. Bugs are usually fixed right away with a patch; for serious bugs, there is almost always a new release. Year 2000 compliance ==================== *MySQL* itself has no problems with Year 2000 compliance: * *MySQL* uses Unix time functions and has no problems with dates until `2069'; all 2-digit years are regarded to be in the range `1970' to `2069', which means that if you store `01' in a `year' column, *MySQL* treats it as `2001'. * All *MySQL* date functions are stored in one file `sql/time.cc' and coded very carefully to be year 2000-safe. * In *MySQL* 3.22 and later versions, the new `YEAR' column type can store years `0' and `1901' to `2155' in 1 byte and display them using 2 or 4 digits. You may run into problems with applications that use *MySQL* in a way that is not Year 2000-safe. For example, many old applications store or manipulate years using 2-digit values (which are ambiguous) rather than 4-digit values. This problem may be compounded by applications that use values such as `00' or `99' as "missing" value indicators. Unfortunately, these problems may be difficult to fix, since different applications may be written by different programmers, each of whom may use a different set of conventions and date-handling functions. Here is a simple test that shows that MySQL doesn't have any problems with dates until 2030 ! mysql> DROP TABLE IF EXISTS y2k; mysql> CREATE TABLE y2k (date date, date_time datetime, time_stamp timestamp); mysql> INSERT INTO y2k VALUES ("1998-12-31","1998-12-31 23:59:59",19981231235959); mysql> INSERT INTO y2k VALUES ("1999-01-01","1999-01-01 00:00:00",19990101000000); mysql> INSERT INTO y2k VALUES ("1999-09-09","1999-09-09 23:59:59",19990909235959); mysql> INSERT INTO y2k VALUES ("2000-01-01","2000-01-01 00:00:00",20000101000000); mysql> INSERT INTO y2k VALUES ("2000-02-28","2000-02-28 00:00:00",20000228000000); mysql> INSERT INTO y2k VALUES ("2000-02-29","2000-02-29 00:00:00",20000229000000); mysql> INSERT INTO y2k VALUES ("2000-03-01","2000-03-01 00:00:00",20000301000000); mysql> INSERT INTO y2k VALUES ("2000-12-31","2000-12-31 23:59:59",20001231235959); mysql> INSERT INTO y2k VALUES ("2001-01-01","2001-01-01 00:00:00",20010101000000); mysql> INSERT INTO y2k VALUES ("2004-12-31","2004-12-31 23:59:59",20041231235959); mysql> INSERT INTO y2k VALUES ("2005-01-01","2005-01-01 00:00:00",20050101000000); mysql> INSERT INTO y2k VALUES ("2030-01-01","2030-01-01 00:00:00",20300101000000); mysql> INSERT INTO y2k VALUES ("2050-01-01","2050-01-01 00:00:00",20500101000000); mysql> SELECT * FROM y2k; +------------+---------------------+----------------+ | date | date_time | time_stamp | +------------+---------------------+----------------+ | 1998-12-31 | 1998-12-31 23:59:59 | 19981231235959 | | 1999-01-01 | 1999-01-01 00:00:00 | 19981231000000 | | 1999-09-09 | 1999-09-09 23:59:59 | 19990909235959 | | 2000-01-01 | 2000-01-01 00:00:00 | 20000101000000 | | 2000-02-28 | 2000-02-28 00:00:00 | 20000228000000 | | 2000-02-29 | 2000-02-29 00:00:00 | 20000229000000 | | 2000-03-01 | 2000-03-01 00:00:00 | 20000301000000 | | 2000-12-31 | 2000-12-31 23:59:59 | 20001231235959 | | 2001-01-01 | 2001-01-01 00:00:00 | 20010101000000 | | 2004-12-31 | 2004-12-31 23:59:59 | 20041231235959 | | 2005-01-01 | 2005-01-01 00:00:00 | 20050101000000 | | 2030-01-01 | 2030-01-01 00:00:00 | 20300101000000 | | 2050-01-01 | 2050-01-01 00:00:00 | 00000000000000 | +------------+---------------------+----------------+ 13 rows in set (0.00 sec) mysql> DROP TABLE y2k; This shows that the `DATE' and `DATETIME' types are *Date Data* compliant, while the `TIMESTAMP' type, that is used to store the current time, only has a range up to `2030-01-01'. `TIMESTAMP' has a range of `1970' to `2030' on 32-bit machines. General SQL information and tutorials ===================================== This book has been recommended by a several people on the *MySQL* mailing list: Judith S. Bowman, Sandra L. Emerson and Marcy Darnovsky The Practical SQL Handbook: Using Structured Query Language Second Edition Addison-Wesley ISBN 0-201-62623-3 http://www.awl.com This book has also received some recommendations on the mailing list: Martin Gruber Understanding SQL ISBN 0-89588-644-8 Publisher Sybex 510 523 8233 Alameda, CA USA A SQL tutorial is available on the net at `http://w3.one.net/~jhoffman/sqltut.htm'. Useful *MySQL*-related links ============================ Web development tools that support *MySQL* ------------------------------------------ * PHP: A server-side HTML-embedded scripting language (http://www.php.net/) * A JDBC driver for *MySQL* (http://www.voicenet.com/~zellert/tjFM) * *MySQL* + PHP demos (http://www.wernhart.priv.at/php/) * WWW-SQL: Display database information (http://www.daa.com.au/~james/www-sql/) * Minivend: A Web shopping cart (http://www.minivend.com/minivend/) * HeiTML: A server-side extension of HTML and a 4GL language at the same time (http://www.heitml.com/) * Metahtml: A Dynamic Programming Language for WWW Applications (http://www.metahtml.com/) * VelocityGen for Perl and TCL (http://www.binevolve.com/) * Hawkeye Internet Server Suite (http://hawkeye.net/) * Network Database Connection For Linux (http://www.fastflow.com/) * WDB: Web browser as a universal front end to databases (http://www.lava.net/beowulf/programming/wdb/) * WebGroove Script: HTML compiler and server-side scripting language (http://www.webgroove.com/) * A server-side web site scripting language (http://www.ihtml.com/) * Visual Basic class generator for Active X (http://www.pbc.ottawa.on.ca) * How to use *MySQL* with Coldfusion on Solaris (ftp://ftp.igc.org/pub/myodbc/README) Web servers with *MySQL* tools ------------------------------ * An Apache authentication module (http://bourbon.netvision.net.il/mysql/mod_auth_mysql/) * The Roxen Challenger Web server (http://www.roxen.com/) Examples and source ------------------- * Examples using *MySQL* (http://php.netvision.net.il/examples), * A Contact Database using *MySQL* and PHP (http://www.webtechniques.com/features/1998/01/note/note.shtml) * Web based interface and Community Calender with PHP (http://modems.rosenet.net/mysql/) * Perl package to generate html from a SQL table structure and for generating SQL statements from an html form. (http://www.odbsoft.com/cook/sources.htm) * Basic telephone database using `DBI'/`DBD' (http://www.gus.ml.org/proj/telsql/). * *TmySQL*; A library to use *MySQL* with Delphi (http://www.productivity.org/projects/mysql/) Other *MySQL*-related links --------------------------- * Links about using *MySQL* in Japan/Asia (http://www.softagency.co.jp/mysql/index.en.phtml) * Commercial Web defect tracking system (http://www.open.com.au/products.html) * PTS: Project Tracking System (http://www.stonekeep.com/pts/) * Job and software tracking system (http://tomato.nvgc.vt.edu/~hroberts/mot) * Support for BIND (The Internet Domain Name Server) (http://www.seawood.org/msql_bind/) * Registry of Web providers who support *MySQL* (http://www.wix.com/mysql-hosting) * Full-text search engine using *MySQL* (http://home.wxs.nl/cgi-bin/planeteers/pgidszoek.cgi) * ExportSQL: A script to export data from Access95+ (http://www.cynergi.net/non-secure/exportsql/) * SAL (Scientific Applications on Linux) *MySQL* entry (http://SAL.KachinaTech.COM/H/1/MYSQL.html) * *MySQL* Apps and Utilities Listing (http://www.cgishop.com/bin/mysqllist) * A consulting company which mentions *MySQL* in the right company (http://www.infotech-nj.com/itech/index.shtml) * PMP Computer Solutions. Database developers using *MySQL* and `mSQL' (http://www.pmpcs.com/) * Airborne Early Warning Association (http://www.aewa.org) * *MySQL* UDF Registry (http://abattoir.cc.ndsu.nodak.edu/~nem/mysql/udf/) SQL and database interfaces --------------------------- * The JDBC database access API (http://java.sun.com/products/jdbc/) * *MySQL* binding to Free Pascal (http://tfdec1.fys.kuleuven.ac.be/~michael/fpc-linux/mysql) * Patch for `mSQL' TCL (http://www.gagme.com/mysql) * EasySQL: An ODBC-like driver manager (http://www.amsoft.ru/easysql/) * A REXX interface to SQL databases (http://www.lightlink.com/hessling/rexxsql.html) * TCL interface (http://www.binevolve.com/~tdarugar/tcl-sql) * Example of storing/retrieving images with *MySQL* and CGI (http://tim.desert.net/~tim/imger/) General database links ---------------------- * Database Jump Site (http://www.pcslink.com/~ej/dbweb.html) * Homepage of the webdb-l (Web Databases) mailing list. (http://black.hole-in-the.net/guy/webdb/) * Perl `DBI'/`DBD' modules homepage (http://www.hermetica.com/technologia/DBI/) * Cygwin tools (MySQL +Apache + PHP under Win32 (http://www-public.rz.uni-duesseldorf.de/~tolj) There are also many web pages that use *MySQL*. *Note Users::. Send any additions to this list to . *MySQL* mailing lists and how to ask questions or report errors (bugs) ********************************************************************** The *MySQL* mailing lists ========================= Requests to be added to or dropped from the main *MySQL* mailing list should be sent to the electronic mail address . Sending a one-line message saying either `subscribe mysql' or `unsubscribe mysql' suffices. If your reply address is not valid, you may specify your address explicitly using `subscribe mysql your-name@your.domain' or `unsubscribe mysql your-name@your.domain'. Please *do not* send mail about subscribing or unsubscribing to , since any mail sent to that address is forwarded automatically to hundreds of other users. Your local site may have many subscribers to . If so, it may have a local mailing list, so that a single message from `tcx.se' is sent to the site and propagated to the local list. In such cases, please contact your system administrator to be added to or dropped from the local *MySQL* list. Mail to is handled automatically by the Majordomo mailing list processor. The following *MySQL* mailing lists exist: `mysql-announce' This is for announcement of new versions of *MySQL* and related programs. This is a low volume list that we think all *MySQL* users should be on. `mysql' The main list for general *MySQL* discussion. Please note that some things should go to the more-specialized lists. It you post to the wrong list, you may not get an answer! `mysql-digest' The `mysql' list in digest form. That means you get all individual messages, sent as one large mail message once a day. `mysql-Java' Discussion about *MySQL* and Java. Mostly about the JDBC drivers. `mysql-win32' All things concerning *MySQL* on Microsoft operating systems like Windows/NT. `myodbc' All things concerning connecting to *MySQL* with ODBC. `msql-mysql-modules' A list about the Perl support in *MySQL*. `msql-mysql-modules-digest' A digest version of the `msql-mysql-modules' list. `mysql-developer' A list for people who work on the *MySQL* code. You subscribe or unsubscribe to all lists in the same way as described above. In your subscribe or unsubscribe request, just put the appropriate mailing list name rather than `mysql'. Asking questions or reporting bugs ================================== Before you ask a question on the mailing list, it is a good idea to check this manual. If you can't find an answer here, check with your local *MySQL* expert. If you still can't find an answer to your question, go ahead and read the next section about how to send mail to . How to report bugs / problems ============================= Before posting a bug report / question, please start by searching the *MySQL* online manual `http://www.tcx.se/Manual_chapter/manual_toc.html' and in the `MySQL' mail archives. We try to keep the manual up to date and we constantly update this with solutions to new found problems! You can find the some search able mail archives at `http://www.tcx.se/doc.html'. You can also use `http://www.tcx.se/search.html' to search all the web pages (including the manual) at `http://www.tcx.se'. Writing a good bug report takes patience, but doing it right at once saves time from us and from you. This section will help you writing your report right and prevents consuming your time doing things that may not help us much or at all. We encourage everyone to use script `mysqlbug' to generate a bug report, or a report about any problem, if possible. The `mysqlbug' can be found from the `scripts' in the distribution or in the `bin' directory, where you have installed *MySQL*. If you are unable to use it, you should still include all the necessary information from this section. The `mysqlbug' will help you making the report by automatically finding a lot of the following information, but if something important is missing, please include it with your message! Please read carefully this section and make sure you have all the information described here included in your report. Remember that it is possible to answer a letter with too much information, but not the one with too little. Often people omit facts, because they think they know what is the reason for the problem and assume that some details don't matter. A good principle is: if you are in doubt to state something, state it! It is a thousand times faster and less troublesome to read a couple of lines more than to be forced to ask again and wait for the answer. Most common errors are that people don't tell the *MySQL* version number they are using, or don't tell on what platform they have *MySQL* installed on, including the version number of the platform. This is very relevant information and in 99 cases out of 100 the bug report is useless without this information! Very often we get questions like 'Why doesn't this work for me?' and then we found that the quested feature wasn't yet implemented to that *MySQL* version, or there was a bug which was already fixed in the newer *MySQL* versions. Sometimes the error is platform depended and it is next to impossible to fix anything without knowing the operating system and the version number of the platform. Remember also to give information about your compiler, if it is related to the problem. Often people found bugs in compilers and think the problem is *MySQL* related. Most compilers are under development all the time and become better version by version too. To verify, if the problem depends on compiler, we need to know what compiler is used. Note that every compiling problem should be regarded as a bug report and reported according to it. Most helpful is when a good description of the problem is given. That is, a good example of all the things one did that leaded to the problem and the problem itself exactly described. The best bug reports are those that includes a full example how to reproduce the bug or problem. If a program gives an error message, please include it. If we try to search something from the archives using programs, it is better that the error message is exactly the one that the program gave. (Even the case sensitivity should be observed!) This is the reason why >>cut'n'paste>> is the only right principle here! * Version number of the *MySQL* you are using (for example, *MySQL* 3.22.12). You can find out which version you are running by executing `mysqladmin version'. `mysqladmin' can be found from the `bin' directory where *MySQL* is installed. * The manufacturer and model of the machine you are working on. * The operating system name and version. For most operating systems, you can get this by executing a Unix command `uname -a'. * Sometimes the amount of memory is relevant. (real and virtual) If in doubt, include them. * If one has the source distribution of *MySQL*, the information about the compiler used is needed. The name and the version number. If one has a binary distribution, the distribution name is needed. * If the problem occurs during a compilation, include the exact error message(s) and also a few lines around the offending code in the file where the error occurred. * Include the output from `mysqldump --no-data database table1 table2...', if any table is related to the problem. This is very easy and a powerful way to get information about any table in a database and we will be able to create a situation that matches the one you have. * In speed related bugs/problems with selects, one should always include the output of 'explain select ...' and at least the number of rows that the 'select ...' gives. * If a problem / bug occurs while running *MySQL*, an input script, which will reproduce the bug, is needed. This script should include all the necessary source files, if any. The closer to the real situation the script will make, the better. * If you think that *MySQL* gives a strange result from a query, include not only the result, but also your opinion what the result should be and some account for why. * When giving an example of the problem, it's better to use same variable names, table names, etc. those exist in the real situation than come up with new names. The problem could be even a variable, table etc. name related! Rare case perhaps, but better safe than sorry. After all it should be easier for you to use the same situation in your example that you really had and it is by all means better for us. In case you have some data you don't want to show to others, you can use `ftp' to transfer the data to `ftp://www.tcx.se/pub/mysql/secret'. If the data is really top secret and you don't want to show it even to us, then go ahead and make an example using other variable names, etc., but please regard it as the last choice. * If a program gives an error message, it is very important to state it! One should never try to remember what the error message was, but copy and paste the whole error message into the mail! * Include all the options given to the relevant programs, if possible. For example, the options to the mysqld daemon and to any *MySQL* client programs. The options to `mysqld' ,`mysql' or to `configure' script are often keys to answers and very relevant! It is never a bad idea to include them anyway! If you use any modules, like Perl or PHP, please include the version number(s) of these. * If you can't produce a test case in a few rows, or if the test table is too big to be mailed to everyone (more than 10 rows), you should dump your tables using `mysqldump' and create a `README' file that describes your problem. Use `tar' and `gzip' or `zip' on the files and use `ftp' to transfer the archive to `ftp://www.tcx.se/pub/mysql/secret'. Then send a short description of the problem to . * If your question is related to the privilege system, please include the output of `mysqlaccess' (can be found from the scripts directory), the output of `mysqladmin reload' and all the error messages you get when trying to connect! You should do all the tests in the order above! * If you have a patch for a bug, it's good. If the patch is good, then very good. Still, don't expect that we will use the patch anyway and omit some necessary information, like a test case, thinking that the patch is all we need. We might found problems with your patch or don't understand it at all and if so, we don't use the patch. If we can't verify what the patch is exactly meant for, we don't use it. A test case will help us here. Show that the patch will handle all the situations that may happen. If we found, even a rare borderline case, there the patch won't work, the patch may be useless. * A guess about what the bug is, why it occurs, or what it depends on, is usually wrong. Even we can't guess such things without first using a debugger to find out where the bug really comes from. * Indicate in your mail message that you have checked the reference manual and mail archive so others know that you have tried to solve your problem yourself. * If you get a `parse error' please check your syntax closely! If you can't find something wrong with it, it's extremely likely that your current version of *MySQL* doesn't support the query you are using! In this case you should check the *MySQL* change history for when the syntax was implemented! *Note News:: If the manual at `http://www.tcx.se/doc.html' doesn't cover the query syntax you are using, this means that *MySQL* doesn't yet support this! In this case your only options are to implement this yourself or email and ask for an offer to implement this! * If possible download the newest *MySQL* version and test if your problem is solved in this! All *MySQL* versions are throughly tested and should work without problems! We believe in making everything as backward compatible as possible and you should be able to switch *MySQL* version in minutes! *Note Which version::. If you are a support customer, please cross post the bug report to for higher priority treatment, as well as to the appropriate mailing list to see if someone else has experienced (and perhaps solved) the problem. For information on reporting bugs in *MyODBC*, see *Note ODBC Problems::. When answers are sent to you individually and not to the mailing list, it is considered good etiquette to summarize the answers and send the summary to the mailing list to that others may have the benefit of the responses you received that helped you solve your problem!. What to do if *MySQL* keeps crashing ------------------------------------ Since it is very hard to know why something is crashing, first try to check whether or not things that work for others crash for you. Please try the following things: * Have you tried the benchmarks? This should test *MySQL* rather well. You can also add code that simulates your application! * Try `fork_test.pl' and `fork2_test.pl'. * If you configure *MySQL* for debugging, it will be much easier to find out possible errors if something goes wrong. *Note Debugging::. * Reconfigure *MySQL* with the `--with-debug' option to `configure' and then recompile. This causes a safe memory allocator to be included that can find some errors. It also provides a lot of output about what is happening. * Use `mysqld --log' and try to determine from the information in the log whether or not some specific query kills the server. 95% of all bugs are related to some specific query! * Have you applied the latest patches for your operating system? * Use the `--skip-locking' option to `mysqld'. On some systems, the `lockd' lock manager does not work properly; the `--skip-locking' option tells `mysqld' not to use external locking. (This means that you cannot run 2 `mysqld' servers on the same data and you must be careful when using `isamchk', but it may be instructive to try the option as a test.) * Have you tried `mysqladmin -u root processlist' when `mysqld' appears to be dead? Sometimes `mysqld' is not dead even though you might think so. The problem may be that all connections are in use, or there may be some internal lock problem. `mysqladmin processlist' will usually be able to make a connection even in these cases, and can provide useful information about the current number of connections and their status. * Run the command `mysqladmin -i 5 status' in a separate window to output statistics. * Try the following: 1. Start `mysqld' from `gdb' (or another debugger). 2. Run your test scripts. 3. Do `back' (or the backtrace command in your debugger) when `mysqld' core dumps. * Try to simulate your application with a Perl script to force *MySQL* to crash or misbehave. * Or send a normal bug report. *Note Bug reports::. But be even more detailed than usual. Since *MySQL* works for many people it may be that the crash results from something that exists only on your computer (for example, an error that is related to your particular system libraries). Guidelines for answering questions on the mailing list ====================================================== If you consider your answer to have broad interest, you may want to post it to the mailing list instead of replying directly to the individual who asked. Try to make your answer general enough that people other than the original poster may benefit from it. When you post to the list, please make sure that your answer is not a duplication of a previous answer. Try to summarize the essential part of the question in your reply, but don't feel obliged to quote the whole question. Please don't post mails from your browser with HTML mode turned on! Many users doesn't read mails with a browser! Licensing or When do I have/want to pay for *MySQL*? **************************************************** The basic licensing issues are: * The easiest way to pay for *MySQL* is to use the license form at TcX's secure server at `https://www.tcx.se/license.htmy'. * We hope everybody understands that you only have to pay if you are selling *MySQL* directly, selling a product which includes the *MySQL* server or installing and maintaining a *MySQL* server at some client site. You may not include *MySQL* in a distribution if you charge for some part of the distribution. For internal use, you do not have to pay us if you do not want to. * There is no restriction in the number of clients that connects to a *MySQL* server or the number of *MySQL* servers that runs on one machine! * You do not need a license to include client code in commercial programs. The client access part of *MySQL* is in the public domain. The command line client (`mysql') includes parts that are under the GNU Public License (`readline'). * We may add some additional functionality in the commercial version. The likely test candidate for this is the ability to create fast compressed read-only databases. The current server includes support to read such databases but not the packing tool used to create them. If we get enough revenue from support, we will probably release this under the same license as the other stuff. * But if you like *MySQL* and want to encourage further development you are welcome to purchase a license or support. *Note Public license::. How much *MySQL* costs ====================== For normal use on Unix or OS/2, *MySQL* costs nothing. When you sell *MySQL*, directly or as a part of another product, you have to pay for it. *Note Public license::. For use on Win95/Win98/NT you will need a *MySQL* license after a trial time of 30 days. You can of course first try the shareware version before buying! `http://www.tcx.se/mysql_w32.htmy,*MySQL* -Win32' Some examples about when you need a `MySQL' license on Unix / OS/2. * If you use *MySQL* to store data for www server you don't have to pay for a license. * If a customer sets and administrates a *MySQL* server on your machine for himself, neither you or he needs a *MySQL* license. * If you set up a *MySQL* server for a paying client you will need a license for the machine that runs the mysqld server. This is because you are in this case selling a system with `MySQL'. Note that the single *MySQL* license will cover any number of users/customers on this machine! * If you on install *MySQL* on a clients machine and any money changes hands (directly or indirectly) then you must buy a *MySQL* license! * If you sell a product, that will be installed at the customers machine, that REQUIRES *MySQL* to work, you will need a license. *Note User adding MySQL::. If your use of *MySQL* requires a license (*note Licensing and Support::.), you only need to get a license for each machine that runs the `mysqld' server. A multi-CPU machine counts as one machine. There is no restriction on the number of concurrent users connected to a machine running a `mysqld' server. Our current license prices are shown below. All prices are in US Dollars. If you pay by credit card, the currency is EURO (European Union Euro) so the prices will differ slightly. *Number of *Price per *Total* licenses* copy* 1 US $200 US $200 10 pack US $150 US $1500 50 pack US $120 US $6000 For high volume (OEM) purchases, the following prices apply: *Number of *Price per *Minimum at one time* *Minimum payment* licenses* copy* 100-1000 $40 100 $4000 1000-2500 $25 200 $5000 2500-5000 $20 400 $8000 For OEM purchases, you must act as a middle-man for eventual problems or extension requests from users. We also require OEM customers to have a support contract. If you have a low-margin high-volume product, you can always talk to us about other terms (for example, a percent of the sale price). If you do, please be informative about your product, pricing, market and any other information that may be relevant. How to get commercial support ============================= A full-price license includes really basic support. This means that we try to answer any relevant question. If the answer is in the documentation, we will direct you to the appropriate section. If you do not have a license or support, we probably will not answer at all. If you discover what we consider a real bug, we are likely to fix it in any case. But if you pay for support we will notify you about the fix status instead of just fixing it in a later release. More comprehensive support is sold separately. Costs for the various types of commercial support are shown below, and the following sections describe what each level of support includes. You are entitled to upgrade from any lower level of support to a higher level of support for the difference between the prices of the two support levels. Support level prices are in EURO (European Union Euro). One EURO is about 1.17 USD. *Type of support* *Cost per year* Basic email support EURO 170 Extended email EURO 1000 support Login support EURO 2000 Extended login EURO 5000 support Basic email support ------------------- Basic email support includes the following types of service: * For *MySQL*-specific questions that don't belong on the *MySQL* mailing list (), you can contact . Remember to always include your registration number and expiration date to ensure a quick response from . You can also crosspost your questions to any of the standard *MySQL* mailing lists, as someone else may already have experienced and solved the problem/question you have. * If your question is already answered in the manual, we will inform you of the correct section in which you can find the answer. If the answer is not in the manual, we will point you in the right direction to solve your problem. * We guarantee a timely answer for your email messages. We can't guarantee that we can solve any problem, but at least you will receive an answer if we can contact you by email. * We will help with unexpected problems when you install *MySQL* from a binary distribution on supported platforms. This level of support does not cover installing *MySQL* from a source distribution. * We will help you with bugs and missing features. Any bugs that are found are fixed for the next *MySQL* release. If the bug is critical for you, we will mail you a patch for it as soon the bug is fixed. Critical bugs always have the highest priority for us, to ensure that they are fixed as soon as possible. * Your suggestions for the further development of *MySQL* will be taken into consideration. By taking email support you have already helped the further development of *MySQL*. If you want to have more input, upgrade to a higher level of support. * If you want us to help optimize your system, you have to upgrade to a higher level of support. Basic email support is a very inexpensive support option and should be thought of more as a way to support our development of *MySQL* than as a real support option. Extended email support ---------------------- Extended basic support includes everything in basic email support with these additions: * Your email will be dealt with before mail from basic email support users and non-registered users. * Your suggestions for the further development of *MySQL* will receive strong consideration. Simple extensions that suit the basic goals of *MySQL* are implemented in a matter of days. By taking extended email support you have already helped the further development of *MySQL*. * We include a binary version of the `pack_isam' tool that supports fast compressed read-only databases (no `BLOB' or `TEXT' types yet). The current server includes support to read such databases but not the packing tool. * Typical questions that are covered by extended email support are: - We will answer and (within reason) solve questions that relate to possible bugs in *MySQL*. As soon as the bug is found and corrected, we will mail a patch for it. - We will help with unexpected problems when you install *MySQL* from a source or binary distribution on supported platforms. - We will answer questions about missing features and offer hints how to work around them. - We will provide hints on optimizing `mysqld' for your situation. * You are allowed to influence the priority of items on the *MySQL* TODO. This will ensure that the features you really need will be implemented sooner than they might be otherwise. Login support ------------- Login support includes everything in extended basic email support with these additions: * Your email will be dealt with even before mail from extended support users. * Your suggestions for the further development of *MySQL* will be taken into very high consideration. Realistic extensions that can be implemented in a couple of hours and that suit the basic goals of *MySQL* will be implemented as soon as possible. * If you have a very specific problem, we can try to log in on your system to solve the problem "in place". * Like any database vendor, we can't guarantee that we can rescue any data from crashed tables, but if the worst happens we will help you rescue as much as possible. *MySQL* has proven itself very reliable, but anything is possible due to circumstances beyond our control (for example, if your system crashes or someone kills the server with `kill -9'). * We will provide hints on optimizing your system and your queries. * You are allowed to call a *MySQL* developer (in moderation) and discuss your *MySQL*-related problems. Extended login support ---------------------- Extended login support includes everything in login support with these additions: * Your email has the highest possible priority. * We will actively examine your system and help you optimize it and your queries. We may also optimize and/or extend *MySQL* to better suit your needs. * You may also request special extensions just for you. For example: mysql> select MY_CALCULATION(col_name1,col_name2) from tbl_name; * We will provide a binary distribution of all important *MySQL* releases for your system, as long as we can get an account on a similar system. In the worst case, we may require access to your system to be able to create a binary distribution. * If you can provide accommodations and pay for traveler fares, you can even get a *MySQL* developer to visit you and offer you help with your troubles. Extended login support entitles you to one personal encounter per year, but we are as always very flexible towards our customers! How to pay for licenses or support ================================== Currently we can take SWIFT payments, cheques or credit cards. Payment should be made to: Postgirot Bank AB 105 06 STOCKHOLM, SWEDEN T.C.X DataKonsult AB BOX 6434 11382 STOCKHOLM, SWEDEN SWIFT address: PGSI SESS Account number: 96 77 06 - 3 Specify: license and/or support and your name and email address. In Europe and Japan you can use EuroGiro (that should be less expensive) to the same account. If you want to pay by cheque, make it payable to "Monty Program KB" and mail it to the address below: T.C.X DataKonsult AB BOX 6434 11382 STOCKHOLM, SWEDEN If you want to pay with credit card over the Internet, you can use TcX's secure license form (https://www.tcx.se/license.htmy). You can also print a copy of the above page, fill it in and send it by fax to: +46-8-729 69 05 If you want us to bill you, you can use the license form and write "bill us" in the comment field. You can also mail a message to with your company information and ask us to bill you. Who to contact for more information about licensing or support ============================================================== For commercial licensing, or if you have any questions about any of the information in this section, please contact: David Axmark Detron HB Kungsgatan 65 B 753 21 UPPSALA SWEDEN Voice Phone +46-18-10 22 80 (Swedish and English spoken) Fax +46-8-729 69 05 (Email *much* preferred) E-Mail: mysql-licensing@tcx.se What copyrights *MySQL* uses ============================ There are several different copyrights on the *MySQL* distribution: 1. The *MySQL*-specific source needed to build the `mysqlclient' library and programs in the `client' directory is in the public domain. Each file that is in the public domain has a header which clearly states so. This includes everything in the `client' directory and some parts of the `mysys', `mystring' and `dbug' libraries. 2. Some small parts of the source (GNU `getopt') are covered by the "GNU LIBRARY LIBRARY GENERAL PUBLIC LICENSE". See the `mysys/COPYING.LIB' file. 3. Some small parts of the source (GNU `readline') are covered by the "GNU GENERAL PUBLIC LICENSE". See the `readline/COPYING' file. 4. Some parts of the source (the `regexp' library) are covered by a Berkeley style copyright. 5. The other source needed for the *MySQL* server on Unix platforms is covered by the "MySQL FREE PUBLIC LICENSE", which is based on the "Aladdin FREE PUBLIC LICENSE." *Note Public license::. When running *MySQL* on any Microsoft operating system, other licensing applies. *Note Win license:: The following points set forth the philosophy behind our copyright policy: * The SQL client library should be totally free so that it can be included in commercial products without limitations. * People who want free access to the software we have put a lot of work into can have it, so long as they do not try to make money directly by distributing it for profit. * People who want the right to keep their own software proprietary, but also want the value from our work, can pay for the privilege. * That means normal in-house use is FREE. But if you use it for something important to you, you may want to support further development of *MySQL* by purchasing a support contract. When you may distribute *MySQL* commercially without a fee ========================================================== This is a clarification of the information in the "*MySQL* FREE PUBLIC LICENSE" (FPL). *Note Public license::. *MySQL* may be *used* freely, including by commercial entities for evaluation or unsupported internal use. However, *distribution* for commercial purposes of *MySQL*, or anything containing or derived from *MySQL* in whole or in part, requires a written commercial license from TcX AB, the sole entity authorized to grant such licenses. You may not include *MySQL* "free" in a package containing anything for which a charge is being made, except as noted below. The intent of the exception provided in the second clause of the license is to allow commercial organizations operating an FTP server or a bulletin board to distribute *MySQL* freely from it, provided that: 1. The organization complies with the other provisions of the FPL, which include among other things a requirement to distribute the full source code of *MySQL* and of any derived work, and to distribute the FPL itself along with *MySQL*; 2. The only charge for downloading *MySQL* is a charge based on the distribution service and not one based on the content of the information being retrieved (i.e., the charge would be the same for retrieving a random collection of bits of the same size); 3. The server or BBS is accessible to the general public, i.e., the phone number or IP address is not kept secret, and anyone may obtain access to the information (possibly by paying a subscription or access fee that is not dependent on or related to purchasing anything else). If you want to distribute software in a commercial context that incorporates *MySQL* and you do *not* want to meet these conditions, you should contact TcX AB to find out about commercial licensing. Commercial licenses involve a payment, and include support and other benefits. These are the only ways you legally can distribute *MySQL* or anything containing *MySQL*: either by distributing *MySQL* under the requirements of the FPL, or by getting a commercial license from TcX AB. Selling a product that can be configured to use *MySQL* ======================================================= If you want to sell a product that can be configured to use *MySQL* although your customer is responsible for obtaining/installing *MySQL* (or some other supported alternative), does one of you owe us money if your customer chooses to use *MySQL*? If your product REQUIRES *MySQL* to work, you would have to buy a license. If *MySQL* just added some new features, it should fall inside normal use. For example, if using *MySQL* added logging to a database rather than to a text file, it would not require a license. This would, of course, mean that the user bears the responsibility of obtaining and installing *MySQL*. If the program is (almost) useless without *MySQL* you would have to get a *MySQL* license to sell your product. Running a commercial web server using *MySQL* ============================================= If you run a commercial web server that uses *MySQL*, you are not selling *MySQL* itself and need not purchase a license. However, in this case we would like you to purchase *MySQL* support. That is either your support of *MySQL* or our support of you (the latter is more expensive since our time is limited). Selling commercial Perl/Tcl/PHP/etc. applications ================================================= These are the questions you should ask to determine whether or not you need a *MySQL* license when selling your application: Is your application designed for *MySQL* alone? Does it require *MySQL* to function at all? Or is it designed more generally for "a database" and can run under *MySQL*, PostgreSQL, or something else? If you've designed it strictly around *MySQL* then you've really made a commercial product that requires the engine, so you need to buy a license. If, however, you can support any database with a base level of functionality (and you don't rely on anything that only *MySQL* supports) you probably DO NOT have to pay. It also depends on what you're doing for the client. Are you tying into a database you expect to already exist by the time your software is purchased? Then you probably don't have to pay. Or do you plan to distribute *MySQL* or give them detailed instructions on installing it with your software? Then you probably do. One thing I'd like to suggest, folks. Look, development won't last forever if nobody pays. I agree that buying a copy for every software user is prohibitive compared to other products available, but would it not be courtesy for commercial developers to register their OWN copy that they develop with? Possible future changes in the licensing ======================================== We may choose to distribute older versions of *MySQL* with the GPL in the future. However, these versions will be identified as *GNU MySQL*. Also, all copyright notices in the relevant files will be changed to the GPL. Installing *MySQL* ****************** How to get *MySQL* ================== Check the *MySQL* home page (http://www.tcx.se/) for information about the current version and for downloading instructions. However, the Internet connection at TcX is not so fast; we would *prefer* that you do the actual downloading from one of the mirror sites listed below. Please report bad or out of date mirrors to . Europe: * Austria [Univ. of Technology/Vienna] WWW (http://gd.tuwien.ac.at/db/mysql/) FTP (ftp://gd.tuwien.ac.at/db/mysql/) * Bulgaria [Naturella] FTP (ftp://ftp.ntrl.net/pub/mirror/mysql) * Czech Republic [CESNET] WWW (http://mirror.opf.slu.cz/mysql/) * Denmark [Ake] WWW (http://mysql.ake.dk) * Denmark [SunSITE] WWW (http://SunSITE.auc.dk/mysql/) FTP (ftp://SunSITE.auc.dk/pub/databases/mysql/) * Estonia [Tradenet] WWW (http://mysql.tradenet.ee) * Germany [Bonn University, Bonn] WWW (http://www.wipol.uni-bonn.de/MySQL//) FTP (ftp://ftp.wipol.uni-bonn.de/pub/mirror/MySQL/) * Germany [Wolfenbuettel] WWW (http://www.fh-wolfenbuettel.de/ftp/pub/database/mysql/) FTP (ftp://ftp.fh-wolfenbuettel.de/pub/database/mysql/) * Germany [Staufen] WWW (http://mysql.staufen.de/) * Greece [NTUA, Athens] WWW (http://www.ntua.gr/mysql/) FTP (ftp://ftp.ntua.gr/pub/databases/mysql/) * Hungary [Xenia] WWW (http://xenia.sote.hu/ftp/mirrors/www.tcx.se-mysql/) * Israel [Netvision] WWW (http://mysql.netvision.net.il/) * Italy [Matrice] WWW (http://www.matrice.it/risorse/mysql/) * Poland [Sunsite] WWW (http://sunsite.icm.edu.pl/mysql/) FTP (ftp://sunsite.icm.edu.pl/pub/unix/mysql/) * Russia [DirectNet] WWW (http://mysql.directnet.ru) * Russia [Cityline] FTP (ftp://mysql.cityline.ru/pub/mysql) WWW (http://mysql.cityline.ru) * Romania [Timisoara] WWW (http://www.dnttm.ro/mysql) FTP (ftp://ftp.dnttm.ro/pub/mysql) * Romania [Bucharest] WWW (http://www.lbi.ro/MySQL) FTP (ftp://ftp.lbi.ro/mirrors/ftp.tcx.se) * Sweden [Sunet] WWW (http://ftp.sunet.se/pub/unix/databases/relational/mysql/) FTP (ftp://ftp.sunet.se/pub/unix/databases/relational/mysql/) * UK [Omnipotent/UK] WWW (http://mysql.omnipotent.net/) FTP (ftp://mysql.omnipotent.net/) * UK [PLiG/UK] WWW (http://ftp.plig.org/pub/mysql/) FTP (ftp://ftp.plig.org/pub/mysql/) * UK [SunSITE] WWW (http://sunsite.org.uk/packages/mysql/) FTP (ftp://sunsite.org.uk/packages/mysql/) * Ukraine [PACO] WWW (http://mysql.paco.net.ua) FTP (ftp://mysql.paco.net.ua/) North America: * Canada [Polaris Computing] WWW (http://mysql.polaris.ca/) * Canada [Tryc] WWW (http://web.tryc.on.ca/mysql/) * Canada [Cyberus] WWW (http://mysql.cyberus.ca/) FTP (ftp://mysql.cyberus.ca/) * USA [Hurricane Electric/San Jose] WWW (http://mysql.he.net) * USA [Buoy/New York] WWW (http://www.buoy.com/mysql/) * USA [Netcasting/West Coast] FTP (ftp://ftp.netcasting.net/pub/mysql/) * USA [Circle Net/North Carolina] WWW (http://www.mysql.net) * USA [Gina net/Florida] WWW (http://www.gina.net/mysql/) * USA [DIGEX] FTP (ftp://ftp.digex.net/pub/database/mysql/index.html) South America: * Chile [Amerikanclaris] WWW (http://www.labs.amerikanclaris.cl/mysql) FTP (ftp://ftp.amerikanclaris.cl/pub/mysql) Asia: * Korea [KREONet] WWW (http://linux.kreonet.re.kr/mysql/) * Japan [Soft Agency] WWW (http://www.softagency.co.jp/MySQL) * Japan [Nagoya Syouka University] WWW (http://www.happysize.co.jp/mysql/) FTP (ftp://ftp.happysize.co.jp/pub/mysql/) * Japan [HappySize] WWW (http://mirror.nucba.ac.jp/mirror/mysql) FTP (ftp://mirror.nucba.ac.jp/mirror/mysql) * Singapore [Com5 Productions] WWW (http://mysql.com5.net) FTP (ftp://ftp.com5.net/pub/mysql) * Taiwan [NCTU] WWW (http://mysql.taconet.com.tw) Australia: * Australia [AARNet/Queensland] WWW (http://mirror.aarnet.edu.au/mysql) FTP (ftp://mirror.aarnet.edu.au/pub/mysql) * Australia [Tas] WWW (http://ftp.tas.gov.au/mysql) FTP (ftp://ftp.tas.gov.au/pub/mysql) * Australia [Blue Planet/Melbourne] WWW (http://mysql.bluep.com/) FTP (ftp://mysql.bluep.com/pub/mirror1/mysql/) Africa: * South-Africa [The Internet Solution/Johannesburg] FTP (ftp://ftp.is.co.za/linux/mysql/) Operating systems supported by *MySQL* ====================================== We use GNU Autoconf so it is possible to port *MySQL* to all modern systems with working Posix threads and a C++ compiler. The client code requires C++ but not threads. We use and develop the software ourselves primarily on Sun Solaris (versions 2.5 & 2.6) and to a lesser extent on RedHat Linux 5.0. *MySQL* has been reported to compile sucessfully on the following operating system/thread package combinations. Note that for many operating systems, the native thread support works only in the latest versions. * Solaris 2.5, 2.6 and 2.7 with native threads on sparc and x86 * SunOS 4.x with the included MIT-pthreads package * BSDI 2.x with the included MIT-pthreads package * BSDI 3.0 and 3.1 with native threads * SGI IRIX 6.x with native threads * AIX 4.x with native threads * DEC UNIX 4.x with native threads * Linux 2.0+ with LinuxThreads 0.7.1 or `glibc' 2.0.7 * FreeBSD 2.x with the included MIT-pthreads package * FreeBSD 3.x with native threads * SCO OpenServer with a recent port of the FSU-threads package * SCO UnixWare 7.0.1 * NetBSD 1.3 Intel and NetBSD 1.3 Alpha * OpenBSD 2.x with the included MIT-pthreads package * HP-UX 10.20 with the included MIT-pthreads package * Win95 and NT (The newest version is currently available only for users with a *MySQL* license or *MySQL* email support). We have released an older `http://www.tcx.se/mysql_w32.htmy,*MySQL* version (3.21.29) as shareware' for those who like to test before they buy. * OS/2 Which *MySQL* version to use ============================ The first decision to make is whether you want to use the latest development release or the last stable release. Normally if you are beginning to use *MySQL* for the first time or trying to port it to some system for which there is no binary distribution, we recommend going with the development release. This is because there are usually no really bad bugs in the development release, and you can easily test it on your machine with the `crash-me' and benchmark tests. *Note Benchmarks::. Otherwise, if you are running an old system and want to upgrade, but don't want to take chances with 3.22, you should upgrade to 3.21.33. We have tried to fix only fatal bugs and make small, relatively safe changes in this version. The second decision to make is whether you want to use a source distribution or a binary distribution: * If you want to run *MySQL* on a platform for which a current binary distribution exists, use that. It generally will be easier to install than a source distribution. * If you want to read (and/or modify) the C and C++ code that makes up *MySQL*, you should get a source distribution. The source code is always the ultimate manual. Source distributions also contain more tests and examples than binary distributions. In the *MySQL* naming scheme, release numbers consist of three numbers and a suffix. For example, a release name like `mysql-3.21.17-beta' is interpreted like this: * The first number (`3') describes the file format. All version 3 releases have the same file format. When a version 4 appears, every table will have to be converted to the new format (nice tools for this will be included, of course). * The second number (`21') is the release level. Normally there are two to choose from. One is the release/stable branch and the other is the development branch. Normally both are stable but the development version may have quirks, missing documentation or may fail to compile on some systems. * The third number (`17') is the version number within the release level. This is incremented for each new distribution. Usually you want the latest version for the release level you have choosen. * The suffix (`beta') indicates the stability level of the release: - `alpha' means that some new large code section exists which hasn't been 100% tested. Known bugs should be documented in the News section (usually there are none). *Note News::. There are also new commands and extensions in most alpha releases. - `beta' means that all new code has been tested. No major new things are added. There should be no known bugs. - `gamma' is a beta that has been around a while and seems to work fine. This is what many other companies call a release. - If there is no suffix, it means that the version has been run for a while at many different sites with no reports of bugs other than platform-specific bugs. All versions of *MySQL* are run through our standard tests and benchmarks to ensure that they are relatively safe to use. Since the standard tests are extended over time to check for all previously found bugs, the test suite keeps getting better. Note that all releases have been tested at least with: An internal test suite This is part of a production system for a customer. It has many tables with hundreds of megabytes of data. The *MySQL* benchmark suite This runs a range of common queries. It is also a test to see whether the latest batch of optimizations actually made the code faster. *Note Benchmarks::. The `crash-me' test This tries to determine what features the database supports and what its capabilities and limitations are. *Note Benchmarks::. Another test is that we use the newest *MySQL* version in our internal production environment, on at least one machine. We have more than 100 gigabytes of data to work with. How and when updates are released ================================= Well, *MySQL* is evolving quite rapidly here at TcX and we want to share this with other *MySQL* users. We try to make a release when we have a very useful feature that others seem to have a need for. We also try to help out users who request features that are easy to implement. We also take note on what our licensed users want to have and we especially take notes of what our extended email supported customers want and try to help them out. No one has to download a new release. The News section will tell you if the new release has something you really want. *Note News::. We use the following policy when updating *MySQL*: * For each minor update, the last number in the version string is incremented. When there are major new features or minor incompatibilities with previous versions, the second number in the version string is incremented. When the file format changes, the first number is increased. * Stable tested releases are meant to appear about 1-2 times a year, but if small bugs are found, a release with only bug-fixes will be released. * Working releases are meant to appear about every 1-8 weeks. * Binary distributions for some platforms will be made by us for major releases. Other people may make binary distributions for other systems but probably less frequently. * We usually make patches available as soon as we have located and fixed small bugs. * For non-critical but annoying bugs, we will make patches available if they are sent to us. Otherwise we will combine many of them into a bigger patch. * If there is, by any chance, a fatal bug in a release we will make a new release as soon as possible. We would like other companies to do this, too. :) The 3.21.x version incorporates major portability changes for many different systems. When the 3.21 release is stable, we will remove the alpha/beta suffix and move active development to 3.22. Bugs will still be fixed in the stable version. We don't believe in a complete freeze, as this also leaves out bug fixes and things that "must be done". "Somewhat frozen" means that we may add small things that "almost surely will not affect anything that's already working". Installation layouts ==================== This section describes the default layout of the directories created by installing binary and source distributions. A binary distribution is installed by unpacking it at the installation location you choose and creates the following directories in the location you choose (typically `/usr/local/mysql'): *Directory* *Contents of directory* `bin' Client programs, the `mysqld' server `data' Log files, databases `scripts' `mysql_install_db' `share' Error message files `sql-bench' Benchmarks A source distribution is installed after you configure and compile it. By default, the installation step installs files under `/usr/local', in the following subdirectories: *Directory* *Contents of directory* `bin' Client programs and scripts `libexec' The `mysqld' server `share' Error message files `sql-bench' Benchmarks `var' Log files, databases The layout of a source installation differs from that of a binary installation in the following ways: * The `mysqld' server is installed in the `/usr/local/libexec' directory rather than in `/usr/local/mysql/bin'. * The data directory is `/usr/local/var' rather than `/usr/local/mysql/data'. * `mysql_install_db' is installed in the `/usr/local/bin' directory rather than in `/usr/local/mysql/scripts'. Installing a *MySQL* binary distribution ======================================== The basic commands you have to do to use a *MySQL* binary distribution are: shell> bin/mysql_install_db shell> bin/safe_mysqld & Here follows a more detailed description: You need the following tools to install a *MySQL* binary distribution: * GNU `gunzip' to uncompress the distribution. * A reasonable `tar' to unpack the distribution. GNU `tar' is known to work. If you run into problems, *PLEASE ALWAYS USE* `mysqlbug' when posting questions to . Even if the problem isn't a bug, `mysqlbug' gathers system information that will help others solve your problem. By not using `mysqlbug', you lessen the likelihood of getting a solution to your problem! You will find `mysqlbug' in the `bin' directory after you unpack the distribution. *Note Bug reports::. To install a binary distribution, follow the steps below, then proceed to *Note Post-installation::, for post-installation setup and testing. 1. Pick the directory under which you want to unpack the distribution, and move into it. In the example below, we unpack the distribution under `/usr/local' and create a directory `/usr/local/mysql' into which *MySQL* is installed. (The following instructions therefore assume you have permission to create files in `/usr/local'. If that directory is protected, you will need to perform the installation as `root'.) 2. Obtain a distribution file from one of the sites listed in *Note Getting MySQL::. *MySQL* binary distributions are provided as compressed `tar' archives and have names like `mysql-VERSION-OS.tar.gz', where `VERSION' is a number (e.g., `3.21.15'), and `OS' indicates the type of operating system for which the distribution is intended (e.g., `pc-linux-gnu-i586'). 3. Unpack the distribution and create the installation directory: shell> gunzip < mysql-VERSION-OS.tar.gz | tar xvf - shell> ln -s mysql-VERSION-OS mysql The first command creates a directory named `mysql-VERSION-OS'. The second command makes a symbolic link to that directory. This lets you refer more easily to the installation directory as `/usr/local/mysql'. 4. Change into the installation directory: shell> cd mysql You will find several files and subdirectories in the `mysql' directory. The most important for installation purposes are the `bin' and `scripts' subdirectories. `bin' This directory contains client programs and the server You should add the full pathname of this directory to your `PATH' environment variable so that your shell finds the *MySQL* programs properly. `scripts' This directory contains the `mysql_install_db' script used to initialize the server access permissions 5. If you would like to use `mysqlaccess' and have the *MySQL* distribution in some nonstandard place, you must change the location where `mysqlaccess' expects to find the `mysql' client. Edit the `bin/mysqlaccess' script at approximately line 18. Search for a line that looks like this: $MYSQL = '/usr/local/bin/mysql'; # path to mysql executable Change the path to reflect the location where `mysql' actually is stored on your system. If you do not do this, you will get a `broken pipe' error when you run `mysqlaccess'. 6. If you want to install support for the Perl `DBI'/`DBD' interface, see *Note Perl-installation::. 7. If you would like *MySQL* to start automatically when you boot your machine, you can copy `bin/mysql.server' to where your system has its startup files. More information can be found in the `bin/mysql.server' script itself, and in *Note Automatic start::. After everything has been unpacked and installed, you should initialize and test your distribution. *Note Post-installation::. Building client programs ------------------------ If you compile *MySQL* clients that you've written yourself or that you obtain from a third party, they must be linked using the `-lmysqlclient' option on the link command. You may also need to specify a `-L' option to tell the linker where to find the library. For example, if the library is installed in `/usr/local/mysql/lib', use `-L/usr/local/mysql/lib -lmysqlclient' on the link command. For clients that use *MySQL* header files, you may need to specify a `-I' option (for example, `-I/usr/local/mysql/include') when you compile them, so the compiler can find the header files. System-specific notes --------------------- The following sections indicate some of the issues that have been observed to occur on particular systems. Linux notes ........... * *MySQL* needs at least Linux 2.0. * The binary release is linked with `-static', which means you need not worry about which version of the system libraries you have. You need not install LinuxThreads, either. A program linked with `-static' is slightly bigger than a dynamically-linked program but also slightly faster (3-5%). The only problem is that you can't use user definable functions (UDFs) with a statically-linked program. If you are going to write or use UDF functions (this is only something for C or C++ programmers) you must compile *MySQL* yourself, using dynamic linking. * The Linux-Intel binary release of *MySQL* is configured for the highest possible speed. We are even using the Pentium compiler, `pgcc'. This compiler is installed under the name `gcc' and the distribution is configured as follows: shell> CC=gcc \ CFLAGS="-O6 -mpentium -mstack-align-double -fomit-frame-pointer" \ CXX=gcc \ CXXFLAGS="-O6 -mpentium -mstack-align-double -fomit-frame-pointer -felide-constructors" \ ./configure \ --prefix=/usr/local/mysql \ --enable-assembler \ --with-mysqld-ldflags=-all-static * *MySQL* Perl support requires Perl 5.004_03 or newer. HP-UX notes ........... The binary distribution of *MySQL* for HP-UX is distributed as an HP depot file. This means that you must be running at least HP-UX 10.x to have access to HP's software depot tools. The HP version of *MySQL* was compiled on an HP 9000/8xx server under HP-UX 10.20, and uses MIT-pthreads. It is known to work well under this configuration. This version does *not* use HP's native thread package. It is highly unlikely that *MySQL* will use HP native threads on anything but HP-UX 10.30 or later. Other configurations that may work: * HP 9000/7xx running HP-UX 10.20+ * HP 9000/8xx running HP-UX 10.30 (does not use HP native threads) The following configurations almost definitely won't work: * HP 9000/7xx or 8xx running HP-UX 10.x where x < 2 * HP 9000/7xx or 8xx running HP-UX 9.x To install the distribution, use one of the commands below, where `/path/to/depot' is the full path to the depot file: * To install everything, including the server, client and development tools: /usr/sbin/swinstall -s /path/to/depot mysql.full * To install only the server: /usr/sbin/swinstall -s /path/to/depot mysql.server * To install only the client package: /usr/sbin/swinstall -s /path/to/depot mysql.client * To install only the development tools: /usr/sbin/swinstall -s /path/to/depot mysql.developer The depot places binaries and libraries in `/opt/mysql' and data in `/var/opt/mysql'. The depot also creates the appropriate entries in `/sbin/init.d' and `/sbin/rc2.d' to start the server automatically at boot time. Obviously, this entails being `root' to install. Installing a *MySQL* source distribution ======================================== You need the following tools to build and install *MySQL* from source: * GNU `gunzip' to uncompress the distribution. * A reasonable `tar' to unpack the distribution. GNU `tar' is known to work. * A working ANSI C++ compiler. `gcc' >= 2.8.1, `egcs' >= 1.0.2, SGI C++ and SunPro C++ are some of the compilers that are known to work. `libg++' is not needed when using `gcc'. `gcc' 2.7.x has a bug that makes it impossible to compile some perfectly legal C++ files, such as `sql/sql_base.cc'. If you only have `gcc' 2.7.x, you must upgrade your `gcc' to be able to compile *MySQL*. * A good `make' program. GNU `make' is always recommended and is sometimes required. If you have problems, we recommend trying GNU `make' 3.75 or newer. If you run into problems, *PLEASE ALWAYS USE `mysqlbug'* when posting questions to . Even if the problem isn't a bug, `mysqlbug' gathers system information that will help others solve your problem. By not using `mysqlbug', you lessen the likelihood of getting a solution to your problem! You will find `mysqlbug' in the `scripts' directory after you unpack the distribution. *Note Bug reports::. Quick installation overview --------------------------- The basic commands you have to do to install *MySQL* from source are: shell> configure --prefix=/usr/local/mysql shell> make shell> make install shell> scripts/mysql_install_db shell> /usr/local/mysql/bin/safe_mysqld & Here follows a more detailed description: To install a source distribution, follow the steps below, then proceed to *Note Post-installation::, for post-installation initialization and testing. 1. Pick the directory under which you want to unpack the distribution, and move into it. 2. Obtain a distribution file from one of the sites listed in *Note Getting MySQL::. *MySQL* source distributions are provided as compressed `tar' archives and have names like `mysql-VERSION.tar.gz', where `VERSION' is a number like 3.22.14-gamma. 3. Unpack the distribution into the current directory: shell> gunzip < mysql-VERSION.tar.gz | tar xvf - This command creates a directory named `mysql-VERSION'. 4. Change into the top-level directory of the unpacked distribution: shell> cd mysql-VERSION 5. Configure the release and compile everything: shell> ./configure shell> make When you run `configure', you might want to specify some options. Run `./configure --help' for a list of options. *Note `configure' options: configure options, discusses some of the more useful options. If `configure' fails, and you are going to send mail to to ask for assistance, please include any lines from `config.log' that you think can help solve the problem. Also include the last couple of lines of output from `configure' if `configure' aborts. Post the bug report using the `mysqlbug' script. *Note Bug reports::. If the compile fails, see *Note Compilation problems::, for help with a number of common problems. 6. Install everything: shell> make install You might need to run this command as `root'. 7. Create the *MySQL* grant tables shell> scripts/mysql_install_db 8. If you want to install support for the Perl `DBI'/`DBD' interface, see *Note Perl-installation::. 9. If you would like *MySQL* to start automatically when you boot your machine, you can copy `support-files/mysql.server' to where your system has its startup files. More information can be found in the `support-files/mysql.server' script itself, and in *Note Automatic start::. After everything has been installed, you should initialize and test your distribution. You can start the *MySQL* server with: shell> cd mysql-install-directory shell> bin/safe_mysqld & Note that *MySQL* versions before 3.22.10 started the *MySQL* server when you run `mysql_install_db'. This is no longer true! *Note Post-installation::. Applying patches ---------------- Sometimes patches appear on the mailing list. To apply a patch, change into the top-level directory of your *MySQL* source tree and run these commands: shell> gunzip < patch-file-name.gz | patch -p1 shell> rm config.cache shell> make clean Then follow the instructions for a normal source install, beginning with the `./configure' step. After running the `make install' step, restart your *MySQL* server. You may need to bring down any currently running server before you run `make install'. Some systems do not allow you to install a new version of a program if it replaces the version that is currently executing. Typical `configure' options --------------------------- The `configure' script gives you a great deal of control over how you configure your *MySQL* distribution. Typically you do this using options on the `configure' command line. You can also affect `configure' using certain environment variables. For a list of options supported by `configure', run this command: shell> ./configure --help Some of the more commonly-used `configure' options are described below: * To compile just the *MySQL* client libraries and client programs, use the `--without-server' option: shell> ./configure --without-server If you don't have a C++ compiler, `mysql' will not compile (it is the one client program that requires C++). In this case, you can remove the code in `configure' that tests for the C++ compiler and then run `./configure' with the `--without-server' option. The compile step will still try to build `mysql', but you can ignore any warnings about `mysql.cc'. (If `make' stops, try `make -k' to tell it to continue with the rest of the build even if errors occur.) * If you don't want your log files and database directories located under `/usr/local/var', use a `configure' command something like one of these: shell> ./configure --prefix=/usr/local/mysql shell> ./configure --prefix=/usr/local \ --localstatedir=/usr/local/mysql/data The first command changes the installation prefix so that everything is installed under `/usr/local/mysql' rather than the default of `/usr/local'. The second command preserves the default installation prefix, but overrides the default location for database directories (normally `/usr/local/var') and changes it to `/usr/local/mysql/data'. * If you want your sockets located somewhere other than the default location (normally `/tmp' or `/var/run'), use a `configure' command like this: shell> ./configure --with-unix-socket-path=/path/to/socket/dir `/path/to/socket/dir' must be an absolute pathname. * If you want to compile statically-linked programs (e.g., to make a binary distribution, to get more speed or to work around problems with some RedHat distributions), run `configure' like this: shell> ./configure --with-client-ldflags=-all-static \ --with-mysqld-ldflags=-all-static * If you are using `gcc' and don't have `libg++' or `libstdc++' installed, you can tell `configure' to use `gcc' as your C++ compiler: shell> CC=gcc CXX=gcc ./configure When you use `gcc' as your C++ compiler, it will not attempt to link in `libg++' or `libstdc++'. If you get errors that your compiler or linker can't create the shared library `libmysqlclient.so.#' you can work around this problem by giving the `--disable-shared' option to `configure'. In this case, `configure' will not build a shared `libmysqlclient.so.#' library. * You can configure *MySQL* not to use `DEFAULT' column values for non-`NULL' columns (i.e., columns that are not allowed to be `NULL'). This causes `INSERT' statements to generate an error unless you explicitly specify values for all columns that require a non-`NULL' value. To suppress use of default values, run `configure' like this: shell> CXXFLAGS=-DDONT_USE_DEFAULT_FIELDS ./configure * By default, *MySQL* uses the ISO-8859-1 (Latin1) character set. To change the default set, use the `--with-charset' option: shell> ./configure --with-charset=CHARSET `CHARSET' may be one of `big5', `czech', `danish', `dec8', `dos', `german1', `hebrew', `hp8', `hungarian', `koi8_ru', `ru', `latin1', `latin2', `sjis', `swe7', `tis620', `ujis', `usa7' or `win1251'. *Note Character sets::. Note that if you want to change the character set, you must do a `make distclean' between configurations ! If you want to convert characters between the server and the client, you should take a look at the `SET OPTION CHARACTER SET' command. *Note Set option::. *Warning:* If you change character sets after having created any tables, you will have to run `isamchk -r -q' on every table. Your indexes may be sorted incorrectly otherwise. (This can happen if you install *MySQL*, create some tables, the reconfigure *MySQL* using a different character set and reinstall it.) * To configure *MySQL* with debugging code, use the `--with-debug' option: shell> ./configure --with-debug This causes a safe memory allocator to be included that can find some errors and that provides output about what is happening. * Options that pertain to particular systems can be found in the system-specific sections later in this chapter. *Note System-specifics::. Problems compiling? =================== All *MySQL* programs compile cleanly for us with no warnings on Solaris using `gcc'. On other systems, warnings may occur due to differences in system include files. See *Note MIT-pthreads::, for warnings that may occur when using MIT-pthreads. For other problems, check the list below. The solution to many problems involves reconfiguring. If you do need to reconfigure, take note of the following: * If `configure' is run after it already has been run, it may use information that was gathered during its previous invocation. This information is stored in `config.cache'; when `configure' starts up, it looks for that file and reads its contents if it exists, on the assumption that the information is still correct. That assumption is invalid when you reconfigure. * Each time you run `configure', you must run `make' again to recompile. However, you may want to remove old object files from previous builds first, since they were compiled using different configuration options. To prevent old configuration information or object files from being used, run these commands before rerunning `configure': shell> rm config.cache shell> make clean Alternatively, you can run `make distclean'. The list below describes some of the problems compiling *MySQL* that have been found to occur most often: * If you get errors when compiling `sql_yacc.cc' such as the ones shown below, you have probably run out of memory or swap space: Internal compiler error: program cc1plus got fatal signal 11 or Out of virtual memory or Virtual memory exhausted The problem is that `gcc' requires huge amounts of memory to compile `sql_yacc.cc' with inline functions. Try running `configure' with the `--with-low-memory' option: shell> ./configure --with-low-memory This option causes `-fno-inline' to be added to the compile line if you are using `gcc' and `-O0' if you are using something else. You should try the `--with-low-memory' option even if you have so much memory and swap space that you think you can't possibly have run out. This problem has been known to occur even on systems with generous hardware configurations, and the `--with-low-memory' option usually fixes it. * By default, `configure' picks `c++' as the compiler name and GNU `c++' links with `-lg++'. If you are using `gcc', this can cause problems during configuration such as this: configure: error: installation or configuration problem: C++ compiler cannot create executables. You might also observe problems during compilation related to `g++', `libg++' or `libstdc++'. One cause of these problems is that you may not have `g++', or you may have `g++' but not `libg++' or `libstdc++'. The `config.log' contains the exact reason why your c++ compiler didn't work! To work around these problems, you can use `gcc' as your C++ compiler. Try setting the environment variable `CXX' to `"gcc -O3"'. For example: shell> CXX="gcc -O3" ./configure This works because `gcc' compiles C++ sources as well as `g++' does, but does not link in `libg++' or `libstdc++' by default. Another way to fix these problems, of course, is to install `g++', `libg++' and `libstdc++'. * If your compile fails with either of the following errors, you have to upgrade your version of `make' to GNU `make': making all in mit-pthreads make: Fatal error in reader: Makefile, line 18: Badly formed macro assignment or make: file `Makefile' line 18: Must be a separator (: * If your `make' stops with this error, you should try using GNU `make': Can't find Makefile.PL Solaris and FreeBSD are known to have troublesome `make' programs. * If you get error messages from `make' or error messages like this, you have to upgrade your `make' to GNU `make': pthread.h: No such file or directory GNU `make' version 3.75 is known to work. * If you want to define flags to be used by your C or C++ compilers, do so by adding the flags to the `CFLAGS' and `CXXFLAGS' environment variables. You can also specify the compiler names this way using `CC' and `CXX'. For example: shell> CC=gcc shell> CFLAGS=-O6 shell> CXX=gcc shell> CXXFLAGS=-O6 shell> export CC CFLAGS CXX CXXFLAGS See *Note TcX binaries::, for a list of flag definitions that have been found to be useful on various systems. * If you get an error message like this, you need to upgrade your `gcc' compiler: client/libmysql.c:273: parse error before `__attribute__' `gcc' 2.8.1 is known to work, but we recommend using `egcs' 1.0.3a or newer instead. * If you get errors when compiling `mysqld' that look like this, `configure' didn't correctly detect the type of the last argument to `accept()', `getsockname()' or `getpeername()': cxx: Error: mysqld.cc, line 645: In this statement, the referenced type of the pointer value "&length" is "unsigned long", which is not compatible with "int". new_sock = accept(sock, (struct sockaddr *)&cAddr, &length); To fix this, edit the `config.h' file (which is generated by `configure'). Look for these lines: /* Define as the base type of the last arg to accept */ #define SOCKET_SIZE_TYPE XXX Change `XXX' to `size_t' or `int', depending on your operating system. (Note that you will have to do this each time you run `configure', since `configure' regenerates `config.h'.) * The `sql_yacc.cc' file is generated from `sql_yacc.yy'. Normally you don't need to generate `sql_yacc.cc' yourself, since *MySQL* comes with an already-generated copy. However, if you do need to recreate it, you might encounter this error: "sql_yacc.yy", line xxx fatal: default action causes potential... This is a sign that your version of `yacc' is deficient. You probably need to install `bison' (the GNU version of `yacc') and use that instead. * If you need to debug `mysqld' or a *MySQL* client, run `configure' with the `--with-debug' option, then recompile and link your clients with the new client library. Before running a client, you should set the `MYSQL_DEBUG' environment variable: shell> MYSQL_DEBUG=d:t:O,/tmp/client.trace shell> export MYSQL_DEBUG This causes clients to generate a trace file in `/tmp/client.trace'. * If you have problems with your own client code, you should attempt to connect to the server and run your query using a client that is known to work. Do this by running `mysql' in debugging mode: shell> mysql --debug=d:t:O,/tmp/client.trace This will provide useful information in case you mail a bug report. *Note Bug reports::. MIT-pthreads notes ================== This section describes some of the issues involved in using MIT-pthreads. If your system does not provide native thread support, you will need to build *MySQL* using the MIT-pthreads package. This includes most FreeBSD systems, SunOS 4.x, Solaris 2.4 and earlier, and some others. *Note Which OS::. * On most systems, you can force MIT-pthreads to be used by running `configure' with the `--with-mit-threads' option: shell> ./configure --with-mit-threads Building in a non-source directory is not supported when using MIT-pthreads, because we want to minimize our changes to this code. * MIT-pthreads doesn't support the `AF_UNIX' protocol used to implement Unix sockets. This means that if you compile using MIT-pthreads, all connections must be made using TCP/IP (which is a little slower). If you find after building *MySQL* that you cannot connect to the local server, it may be that your client is attempting to connect to `localhost' using a Unix socket as the default. Try making a TCP/IP connection by using `mysql' with a host option (`-h' or `--host') to specify the local host name explicitly. * The checks that determine whether or not to use MIT-pthreads occur only during the part of the configuration process that deals with the server code. If you have configured the distribution using `--without-server' to build only the client code, clients will not know whether or not MIT-pthreads is being used and will use Unix socket connections by default. Since Unix sockets do not work under MIT-pthreads, you will also need to use `-h' or `--host' in such instances. * When *MySQL* is compiled using MIT-pthreads, system locking is disabled by default for performance reasons. You can tell the server to use system locking with the `--use-locking' option. * Sometimes (at least on Solaris) the pthread `bind()' command fails to bind to a socket without any error message. The result is that all connections to the server fail. For example: shell> mysqladmin version mysqladmin: connect to server at '' failed; error: 'Can't connect to mysql server on localhost (146)' The solution to this is to kill the `mysqld' server and restart it. This has only happened to us when we have forced the server down and done a restart immediately. * With MIT-pthreads, the `sleep()' system call isn't interruptible with `SIGINT' (break). This is only noticeable when you run `mysqladmin --sleep'. You must wait for the `sleep()' call to terminate before the interrupt is served and the process stops. * When linking (at least on Solaris) you will receive warning messages like these; they can be ignored: ld: warning: symbol `_iob' has differing sizes: (file /my/local/pthreads/lib/libpthread.a(findfp.o) value=0x4; file /usr/lib/libc.so value=0x140); /my/local/pthreads/lib/libpthread.a(findfp.o) definition taken ld: warning: symbol `__iob' has differing sizes: (file /my/local/pthreads/lib/libpthread.a(findfp.o) value=0x4; file /usr/lib/libc.so value=0x140); /my/local/pthreads/lib/libpthread.a(findfp.o) definition taken * Some other warnings also can be ignored: implicit declaration of function `int strtoll(...)' implicit declaration of function `int strtoul(...)' * We haven't gotten `readline' to work with MIT-pthreads. (This isn't needed, but may be interesting for someone.) Perl installation comments ========================== *MySQL* support for the Perl `DBI'/`DBD' interface is distributed separately from the main *MySQL* distribution, as of release 3.22.8. If you want to install Perl support, check `http://www.tcx.se/Contrib' for the files you will need. The Perl client code for the `DBD'/`DBI' interface requires Perl 5.004 or later. The interface *will not work* if you have an older version of Perl. The Perl distributions are provided as compressed `tar' archives and have names like `MODULE-VERSION.tar.gz', where `MODULE' is the module name and `VERSION' is the version number. You should get the `Data-Dumper', `DBI', and `Msql-Mysql-modules' archives. Once you have them, install them using the procedure shown below. The example shown below is for the `Data-Dumper' module, but the procedure is the same for all three modules. 1. Unpack the distribution into the current directory: shell> gunzip < Data-Dumper-VERSION.tar.gz | tar xvf - This command creates a directory named `Data-Dumper-VERSION'. 2. Change into the top-level directory of the unpacked distribution: shell> cd Data-Dumper-VERSION 3. Build the distribution and compile everything: shell> perl Makefile.PL shell> make shell> make test shell> make install After you've installed the three modules, run `make test' in the `Msql-Mysql-modules' directory to exercise the interface code. (The server must be running for this to work.) Problems using the Perl `DBI'/`DBD' interface --------------------------------------------- If perl reports that it can't find the `../mysql/mysql.so' module, then the problem is probably that perl can't locate the shared library `libmysqlclient.so'. You can fix this by any of the following methods: bullet Compile the Msql-MySQL modules with: `perl Makefile.PL -static' instead of `perl Makefile.PL' bullet Copy `libmysqlclient.so' to the library where your other shared libraries are (probably `/usr/lib' or `/lib'). bullet On `Linux' you can add the path to the directory, where you have `libmysqlclient.so', to `/etc/ld.so.conf'. bullet Add the path to `libmysqlclient.so' to the `LD_RUN_PATH' environment variable. If you get the following errors from `DBD-mysql', you are probably using `gcc' (or using an old binary compiled with `gcc'): /usr/bin/perl: can't resolve symbol '__moddi3' /usr/bin/perl: can't resolve symbol '__divdi3' Add `-L/usr/lib/gcc-lib/... -lgcc' to the link command when the `mysql.so' library gets built (check the output from `make' for `mysql.so' when you compile the Perl client). The `-L' option should specify the path to the directory where `libgcc.a' is located on your system. Another cause of this problem may be that Perl and *MySQL* aren't both compiled with `gcc'. In this case, you can solve the mismatch by compiling both with `gcc'. If you want to use the Perl module on a system that doesn't support dynamic linking (like SCO) you can generate a static version of Perl that includes `DBI' and `DBD-mysql'. The way this works is that you generate a version of Perl with the `DBI' code linked in and install it on top of your current Perl. Then you use that to build a version of Perl that additionally has the `DBD' code linked in, and install that. On SCO, you must have the following environment variables set: shell> LD_LIBRARY_PATH=/lib:/usr/lib:/usr/local/lib:/usr/progressive/lib or shell> LD_LIBRARY_PATH=/usr/lib:/lib:/usr/local/lib:/usr/ccs/lib:/usr/progressive/lib:/usr/skunk/lib shell> LIBPATH=/usr/lib:/lib:/usr/local/lib:/usr/ccs/lib:/usr/progressive/lib:/usr/skunk/lib shell> MANPATH=scohelp:/usr/man:/usr/local1/man:/usr/local/man:/usr/skunk/man: First, you create a Perl that includes a statically-linked `DBI' by running these commands in the `perl/DBI' directory: shell> perl Makefile.PL LINKTYPE=static shell> make shell> make install shell> make perl After this you must install the new Perl. The output of `make perl' will indicate the exact `make' command you will need to execute to perform the installation. On SCO, this is `make -f Makefile.aperl inst_perl MAP_TARGET=perl'. Next you create Perl that includes a statically-linked `DBD::mysql' by running these commands in the `perl/Mysql-modules' directory: shell> perl Makefile.PL LINKTYPE=static shell> make shell> make install shell> make perl You should also install this new Perl. Again, the output of `make perl' indicates the command to use. System-specific notes ===================== The following sections indicate some of the issues that have been observed to occur on particular systems. Solaris notes ------------- On Solaris, you may run into trouble even before you get the *MySQL* distribution unpacked! Solaris `tar' can't handle long file names, so you may see an error like this when you unpack *MySQL*: x mysql-3.22.12-beta/bench/Results/ATIS-mysql_odbc-NT_4.0-cmp-db2,informix,ms-sql,mysql,oracle,solid,sybase, 0 bytes, 0 tape blocks tar: directory checksum error In this case, you must use GNU `tar' (`gtar') to unpack the distribution. You can find a precompiled copy for Solaris at `http://www.tcx.se/Downloads/'. Sun native threads work only on Solaris 2.5 and higher. For 2.4 and earlier versions, *MySQL* will automaticly use MIT-pthreads. *Note MIT-pthreads::. If you have the Sun Workshop 4.2 compiler, you can run `configure' like this: shell> CC=cc CFLAGS="-Xa -fast -xstrconst -mt" \ CXX=CC CXXFLAGS="-xsb -noex -fast -mt" \ ./configure You may also have to edit the `configure' script to change this line: #if !defined(__STDC__) || __STDC__ != 1 to this: #if !defined(__STDC__) If you turn on `__STDC__' with the `-Xc' option, the Sun compiler can't compile with the Solaris `pthread.h' header file. This is a Sun bug (broken compiler or broken include file). If `mysqld' issues the error message shown below when you run it, you have tried to compile *MySQL* with the Sun compiler without enabling the multi-thread option `-mt': libc internal error: _rmutex_unlock: rmutex not held Add `-mt' to `CFLAGS' and `CXXFLAGS' and try again. If you get the following error when compiling *MySQL* with `gcc', it means that your `gcc' is not configured for your version of Solaris! shell> gcc -O3 -g -O2 -DDBUG_OFF -o thr_alarm ... ./thr_alarm.c: In function `signal_hand': ./thr_alarm.c:556: too many arguments to function `sigwait' The proper thing to do in this case is to get the newest version of `egcs' or `gcc' and compile it with your current `gcc' compiler! At least for Solaris 2.5, almost all binary versions of `gcc' have old, unusable include files that will break all programs that use threads (and possibly other programs)! Note that `gcc' 2.8.1 has a couple on bugs on Sparc platforms! On Sparc, we recommend you use `egcs' 1.0.3a. If you are using `egcs' 1.1 or `egcs' 1.1.1 you MUST compile *MySQL* with `-O1' as higher optimization levels produces wrong code. The recommended `configure' line when using `egcs' 1.1 or `egcs' 1.1.1 is: shell> CC=gcc CFLAGS="-O1" \ CXX=gcc CXXFLAGS="-O1 -felide-constructors -fno-exceptions -fno-rtti" \ ./configure --prefix=/usr/local/mysql --with-low-memory As Solaris doesn't provide static versions of all system libraries (`libpthreads' and `libdl'), you can't compile *MySQL* with `--static'. If you try to do this, you will get the error: ld: fatal: library -ldl: not found Solaris 2.7 has some bugs in the include files. If you get the following error when you use `gcc': /usr/include/widec.h:42: warning: `getwc' redefined /usr/include/wchar.h:326: warning: this is the location of the previous definition You can do the following to avoid this: `copy /usr/include/widec.h to .../lib/gcc-lib/os/gcc-version/include' and change row 41 from: #if !defined(lint) && !defined(__lint) to #if !defined(lint) && !defined(__lint) && !defined(getwc) You can of course edit `/usr/include/widec.h' directly. After this you should remove `config.cache' and run `configure' again! If too many processes try to connect very rapidly to `mysqld', you will see this error in the *MySQL* log: Error in accept: Protocol error You might try starting the server with the `--set-variable back_log=50' option as a workaround for this. If you are linking your own *MySQL* client and get the error: ld.so.1: ./my: fatal: libmysqlclient.so.#: open failed: No such file or directory when executing them, the problem can be avoided by one of the following methods: * Link the client with the following flag (instead of `-Lpath'): `-Wl,r/path-libmysqlclient.so' * Copy `libmysqclient.so' to `/usr/lib' * Set the `LD_RUN_PATH' environment to the path to `libmysqlclient.so' before running your client. Solarix x86 notes ----------------- If you are using `gcc' or `egcs' on Solaris x86 and you experience problems with core dumps under load, you should use the following `configure' command: shell> CC=gcc CFLAGS="-O6 -fomit-frame-pointer" \ CXX=gcc \ CXXFLAGS="-O6 -fomit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" \ ./configure --prefix=/usr/local/mysql This will avoid problems with the `libstdc++' library and with C++ exceptions. If this doesn't help, you should compile a debug version and run this with a trace file or under `gdb'. *Note Debugging::. SunOS 4 notes ------------- On SunOS 4, MIT-pthreads is needed. This in turn means you will need GNU `make' to compile *MySQL*. Some SunOS 4 systems have problems with dynamic libraries and `libtool'. You can use the following `configure' line to avoid this problem. ./configure --disable-shared --with-mysqld-ldflags=-all-static When compiling `readline', you may get warnings about duplicate defines. These may be ignored. When compiling `mysqld', there will be some `implicit declaration of function' warnings. These may be ignored. Linux notes (all Linux versions) -------------------------------- If you can't start `mysqld' or if `mysql_install_db' doesn't work, please continue reading! This only happens on Linux system with problems in the LinuxThreads or `libc'/`glibc' libraries. There are a lot of simple workarounds to get *MySQL* to work! The simplest is to use the binary version of *MySQL* (not the RPM) for Linux x86; One nice aspect of this version is that it's probably 10% faster than any version you would compile yourself! *Note Compile and link options::. `isamchk' hangs with `libc.so.5.3.12'. Upgrading to the newest `libc' fixes this problem. When using LinuxThreads you will see a minimum of three processes running. These are in fact threads. There will be one thread for the LinuxThreads manager, one thread to handle connections, and one thread to handle alarms and signals. If you are using LinuxThreads and `mysqladmin shutdown' doesn't work, you have to upgrade to LinuxThreads 0.7.1 or newer. If you are using RedHat, you might get errors like this: /usr/bin/perl is needed... /usr/sh is needed... /usr/sh is needed... If so, you should upgrade your version of `rpm' to `rpm-2.4.11-1.i386.rpm' and `rpm-devel-2.4.11-1.i386.rpm' (or later). You can get the upgrades of libraries to RedHat 4.2 from `ftp://ftp.redhat.com/updates/4.2/i386'. Or `http://www.sunsite.unc.edu/pub/Linux/distributions/redhat/code/rpm/' for other distributions. If you are linking an own *MySQL* client and get the error: ld.so.1: ./my: fatal: libmysqlclient.so.4: open failed: No such file or directory when executing them, the problem can be avoided by one of the following methods: * Link the client with the following flag (instead of `-Lpath'): `-Wl,r/path-libmysqlclient.so' * Copy `libmysqclient.so' to `/usr/lib' * Set the `LD_RUN_PATH' environment to the path to `libmysqlclient.so' before running your client. Linux-x86 notes ............... LinuxThreads should be installed before configuring *MySQL*! *MySQL* requires `libc' version 5.4.12 or newer. It's known to work with `libc' 5.4.46. `glibc' version 2.0.6 and later should also work. There have been some problems with the `glibc' RPMs from RedHat so if you have problems, check whether or not there are any updates! The `glibc' 2.0.7-19 RPM is known to work. On some older Linux distributions, `configure' may produce an error like this: Syntax error in sched.h. Change _P to __P in the /usr/include/sched.h file. See the Installation chapter in the Reference Manual. Just do what the error message says and add an extra underscore to the `_P' macro that has only one underscore, then try again. You may get some warnings when compiling; those shown below can be ignored: mysqld.cc -o objs-thread/mysqld.o mysqld.cc: In function `void init_signals()': mysqld.cc:315: warning: assignment of negative value `-1' to `long unsigned int' mysqld.cc: In function `void * signal_hand(void *)': mysqld.cc:346: warning: assignment of negative value `-1' to `long unsigned int' In Debian GNU/Linux, if you want *MySQL* to start automatically when the system boots, do the following: shell> cp mysql.server /etc/init.d/mysql.server shell> /usr/sbin/update-rc.d mysql.server defaults 99 `mysql.server' can be found in the `share/mysql' directory under the *MySQL* installation directory, or in the `support-files' directory of the *MySQL* source tree. If `mysqld' always core dumps when it starts up, the problem may be that you have an old `/lib/libc.a'. Try renaming it, then remove `sql/mysqld' and do a new `make install' and try again. This problem has been reported on some Slackware installations. RedHat 5.0 has also a similar problem with some new `glibc' versions. *Note Linux-RedHat50::. If you get the following error when linking `mysqld', it means that your `libg++.a' is not installed correctly: /usr/lib/libc.a(putc.o): In function `_IO_putc': putc.o(.text+0x0): multiple definition of `_IO_putc' You can avoid using `libg++.a' by running `configure' like this: shell> CXX=gcc ./configure RedHat 5.0 notes ................ If you have any problems with *MySQL* on RedHat, you should start by upgrading `glibc' to the newest possible version! If you install all the official RedHat patches (including `glibc-2.0.7-19' and `glibc-devel-2.0.7-19'), both the binary and source distributions of *MySQL* should work without any trouble! The updates are needed since there is a bug in `glibc' 2.0.5 in how `pthread_key_create' variables are freed. With `glibc' 2.0.5, you must use a statically-linked *MySQL* binary distribution. If you want to compile from source, you must install the corrected version of LinuxThreads from `http://www.tcx.se/Downloads/Linux' or upgrade your `glibc'. If you have an incorrect version of `glibc' or LinuxThreads, the symptom is that `mysqld' crashes after each connection. For example, `mysqladmin version' will crash `mysqld' when it finishes! Another symptom of incorrect libraries is that `mysqld' crashes at once when it starts. On some Linux systems, this can be fixed by configuring like this: shell> ./configure --with-mysqld-ldflags=-all-static On Redhat 5.0, the easy way out is to install the `glibc' 2.0.7-19 RPM and run `configure' *without* the `--with-mysqld-ldflags=-all-static' option. For the source distribution of `glibc' 2.0.7, a patch that is easy to apply and is tested with *MySQL* may be found at `http://www.tcx.se/Download/Linux/glibc-2.0.7-total-patch.tar.gz'. If you experience crashes like these when you build *MySQL*, you can always download the newest binary version of *MySQL*. This is statically-linked to avoid library conflicts and should work on all Linux systems! *MySQL* comes with an internal debugger that can generate trace files with a lot of information that can be used to find and solve a wide range of different problems. *Note Debugging::. RedHat 5.1 notes ................ The `glibc' of RedHat 5.1 (`glibc' 2.0.7-13) has a memory leak, so to get a stable *MySQL* version, you must upgrade `glibc' to 2.0.7-19, downgrade `glibc' or use a binary version of `mysqld'. If you don't do this, you will encounter memory problems (out of memory, etc., etc.). The most common error in this case is: Can't create a new thread (errno 11). If you are not out of available memory, you can consult the manual for any possible OS dependent bug After you have upgraded to `glibc' 2.0.7-19, you can configure *MySQL* with dynamic linking (the default), but you *cannot* run `configure' with the `--with-mysqld-ldflags=-all-static' option until you have installed `glibc' 2.0.7-19 from source! You can check which version of `glibc' you have with `rpm -q glibc'. Linux-Sparc notes ................. In some implementations, `readdir_r()' is broken. The symptom is that `SHOW DATABASES' always returns an empty set. This can be fixed by removing `HAVE_READDIR_R' from `config.h' after configuring and before compiling. Some problems will require patching your Linux installation. The patch can be found at `http://www.tcx.se/patches/Linux-sparc-2.0.30.diff'. This patch is against the Linux distribution `sparclinux-2.0.30.tar.gz' that is available at `vger.rutgers.edu' (a version of Linux that was never merged with the official 2.0.30). You must also install LinuxThreads 0.6 or newer. Thanks to for this information. Linux-Alpha notes ................. The first problem is LinuxThreads. The RedHat distribution uses an old (broken) LinuxThreads version, so you must patch LinuxThreads for Alpha. Use the following procedure: 1. Obtain the `glibc2.5c' source from any GNU FTP site. 2. Get the file `ftp://www.tcx.se/pub/mysql/linux/patched-glibc-linuxthreads-0.6.tar.gz'. This includes a fixed `.c' file. Copy this to the `glibc' `./linuxthreads' directory. 3. Configure and compile `glibc' (You have to read the manual how to do this together with LinuxThreads), but don't install it! 4. In the `/usr/lib' directory, rename your old version of `libpthread.a' to `libpthread.a-old'. 5. Copy the file `glibc.../linuxthreads/libpthread.a' to `/usr/lib'. 6. Configure *MySQL* with the following command: shell> CC=gcc CCFLAGS="-Dalpha_linux_port" \ CXX=gcc CXXFLAGS="-O3 -Dalpha_linux_port" \ ./configure --prefix=/usr/local/mysql 7. Try to compile `mysys/thr_lock' and `mysys/thr_alarm'. Test that these programs work! (Invoke each one with no arguments. Each should end with `test_succeeded' if everything was okay.) 8. Recompile `mysqld'. Note that Linux-Alpha is still an alpha-quality platform for *MySQL*. With RedHat 5.0 and the patched LinuxThreads, you have a very good chance of it working. If you have problems with signals (*MySQL* dies unexpectedly under high load) you may have found an OS bug with threads and signals. In this case you can tell *MySQL* not to use signals by configuring with: shell> CFLAGS=-DDONT_USE_THR_ALARM CXXFLAGS=-DDONT_USE_THR_ALARM ./configure ... This doesn't affect the performance of *MySQL*, but has the side effect that you can't kill clients that are "sleeping" on a connection with `mysqladmin kill' or `mysqladmin shutdown'. The client will instead die when it issues its next command. MkLinux notes ............. *MySQL* should work on MkLinux with the newest `glibc' package (tested with `glibc' 2.0.7). Linux RPM notes --------------- The recommended way to install *MySQL* on linux is by a RPM. The *MySQL* RPMS is currently being build on a RedHat 5.1 system but should work on other versions of Linux that supports RPM as well. * MySQL-VERSION.i386.rpm The *MySQL* server. Unless you only want to connect to another *MySQL* server running on another machice yo will need this. * MySQL-client-VERSION.i386.rpm The standard *MySQL* client programs. You probably always want to install this package. * MySQL-bench-VERSION.i386.rpm Test and benchmarks. Requires perl and msql-mysql-modules RPMS. * MySQL-devel-VERSION.i386.rpm Libraries and include files nesesarry if you want to compile other *MySQL* clients. * MySQL-VERSION.src.rpm This contains the source code to all of the above packages. It can also be used to try to build RPMS for other architectures (for example, Alpha or SPARC). * To make a standard minimal installation: rpm -i MySQL-VERSION.i386.rpm MySQL-client-VERSION.i386.rpm * To install only the client package: rpm -i MySQL-client-VERSION.i386.rpm The RPM places data in `/var/lib/mysql'. The RPM also creates the appropriate entries in `/sbin/rc.d/' to start the server automatically at boot time. Alpha-DEC-Unix notes -------------------- When compiling threaded programs under Digital UNIX, the documentation recommends the `-pthread' option for `cc' and `cxx' and the libraries `-lmach -lexc' (in addition to `-lpthread'). You should run `configure' something like this: shell> CC="cc -pthread" CXX="cxx -pthread -O" \ ./configure -with-named-thread-libs="-lpthread -lmach -lexc -lc" When compiling `mysqld', you may see a couple of warnings like this: mysqld.cc: In function void handle_connections()': mysqld.cc:626: passing long unsigned int *' as argument 3 of accept(int,sockadddr *, int *)' You can safely ignore these warnings. They occur because `configure' can't detect warnings, only errors. If you start the server directly from the command line, you may have problems with it dying when you log out. (When you log out, your outstanding processes receive a `SIGHUP' signal.) If so, try starting the server like this: shell> nohup mysqld [options] & `nohup' causes the command following it to ignore any `SIGHUP' signal sent from the terminal. Alternatively, start the server by running `safe_mysqld', which invokes `mysqld' using `nohup' for you. Alpha-DEC-OSF1 notes -------------------- If you have problems compiling and have DEC `CC' and `gcc' installed, try running `configure' like this: shell> CC=cc CFLAGS=-O CXX=gcc CXXFLAGS=-O3 \ ./configure --prefix=/usr/local/mysql If you get problems with the `c_asm.h' file, you can create and use a 'dummy' `c_asm.h' file with: shell> touch include/c_asm.h shell> CC=gcc CFLAGS=-I./include CXX=gcc CXXFLAGS="-O3 ./configure --prefix=/usr/local/mysql On OSF1 V4.0D and compiler "DEC C V5.6-071 on Digital UNIX V4.0 (Rev. 878)" the compiler had some strange behavior (undefined `asm' symbols). `/bin/ld' also appears to be broken (problems with `_exit undefined' when linking `mysqld'). On this system, we have managed to compile *MySQL* with the following `configure' line, after replacing `/bin/ld' with the version from OSF 4.0C: shell> CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql In some versions of OSF1, the `alloca()' function is broken. Fix this by removing the line in `config.h' that defines `'HAVE_ALLOCA''. The `alloca()' function also may have an incorrect prototype in `/usr/include/alloca.h'. This warning resulting from this can be ignored. `configure' will use the following thread libraries automatically: `-with-named-thread-libs="-lpthread -lmach -lexc -lc"'. When using `gcc', you can also try running `configure' like this: shell> CFLAGS=-D_PTHREAD_USE_D4 CXX=gcc CXXFLAGS=-O3 ./configure .... If you have problems with signals (*MySQL* dies unexpectedly under high load) you may have found an OS bug with threads and signals. In this case you can tell *MySQL* not to use signals by configuring with: shell> CFLAGS=-DDONT_USE_THR_ALARM CXXFLAGS=-DDONT_USE_THR_ALARM ./configure ... This doesn't affect the performance of *MySQL*, but has the side effect that you can't kill clients that are "sleeping" on a connection with `mysqladmin kill' or `mysqladmin shutdown'. The client will instead die when it issues its next command. SGI-IRIX notes -------------- You may have to undefine some things in `config.h' after running `configure' and before compiling. In some Irix implementations, the `alloca()' function is broken. If the `mysqld' server dies on some `SELECT' statements, remove the lines from `config.h' that define `HAVE_ALLOC' and `HAVE_ALLOCA_H'. If `mysqladmin create' doesn't work, remove the line from `config.h' that defines `HAVE_READDIR_R'. You may have to remove the `HAVE_TERM_H' line as well. Irix 6.2 doesn't support POSIX threads out of of the box. You must install these patches, which are available from SGI if you have support: 1403, 1404, 1644, 1717, 1918, 2000, 2044. If you get the something like the following error when compiling `mysql.cc': "/usr/include/curses.h", line 82: error(1084): invalid combination of type Then type the following in the top-level directory of your *MySQL* source tree: shell> extra/replace bool curses_bool < /usr/include/curses.h > include/curses.h shell> make There have also been reports of scheduling problems. If only one thread is running, things go slow. Avoid this by starting another client. This may lead to a 2-to-10-fold increase in execution speed thereafter for the other thread. This is a poorly-understood problem with IRIS threads; you may have to improvise to find solutions until this can be fixed. If you are compiling with `gcc', you can use the following `configure' command: shell> CC=gcc CXX=gcc CXXFLAGS=-O3 \ ./configure --prefix=/usr/local/mysql --with-thread-safe-client FreeBSD notes ------------- If you notice that `configure' will use MIT-pthreads, you should read the MIT-pthreads notes. *Note MIT-pthreads::. If you get an error on `make install' that it can't find `/usr/include/pthreads', `configure' didn't detect that you need MIT-pthreads on FreeBSD. This is fixed by doing: shell> rm config.cache shell> ./configure --with-mit-threads The FreeBSD `make' behavior is slightly different from that of GNU `make'. If you have `make'-related problems, you should install GNU `make'. If `mysql' or `mysqladmin' takes a long time to respond, a user said the following: Are you running the `ppp' user process? On one FreeBSD box (2.2.5) *MySQL* clients takes a couple of seconds to connect to `mysqld' if the `ppp' process is running. FreeBSD is also known to have a very low default file handle limit. *Note Not enough file handles::. If you have a problem with `SELECT NOW()' returning values in GMT and not your local time, you have to set the `TZ' environment variable to your current timezone. This should be done for the environment in which the server runs, for example, in `safe_mysqld' or `mysql.server'. Make sure that you modify the `/etc/hosts' file so that the `localhost' entry is correct (otherwise you will have problems connecting to the database. The `/etc/hosts' file should start with a line: 127.0.0.1 localhost localhost.your.domain If you are using FreeBSD 2.2.6, don't forget to apply the ttcp and mmap-22 patches to the OS (for security reasons). Please see `http://www.freebsd.org' for these CERT patches. If you are using FreeBSD 2.2.7 and you have problems killing the `mysqld' daemon, you should cvsup new sources and recompile `libc_r'. FreeBSD-3.0 notes ................. You have to run `configure' with the `--with-named-thread-libs=-lc_r' option. The pthreads library for FreeBSD doesn't contain the `sigwait()' function and there are some bugs in it. To fix this, get the `FreeBSD-3.0-libc_r-1.0.diff' file and apply this in the `/usr/src/lib/libc_r/uthread' directory. Then follow the instructions that can be found with `man pthread' about how to recompile the `libc_r' library. You can test if you have a "modern" `libpthread.a' with this command: shell> nm /usr/lib/libc_r.a | grep sigwait If the above doesn't find `sigwait', you must use the patch above and recompile `libc_r'. BSD/OS 2.# notes ---------------- If you get the following error when compiling *MySQL*, your ulimit for virtual memory is too low: item_func.h: In method `Item_func_ge::Item_func_ge(const Item_func_ge &)': item_func.h:28: virtual memory exhausted make[2]: *** [item_func.o] Error 1 Try using `ulimit -v 80000' and run `make' again. If this doesn't work and you are using `bash', try switching to `csh' or `sh'; Some BSDI users have reported problems with `bash' and `ulimit'. If you are using `gcc', you may also use have to use the `--with-low-memory' flag to configure to be able to compile `sql_yacc.cc'. If you have a problem with `SELECT NOW()' returning values in GMT and not your local time, you have to set the `TZ' environment variable to your current timezone. This should be done for the environment in which the server runs, for example in `safe_mysqld' or `mysql.server'. BSD/OS 3.# notes ................ 1. Upgrade to BSD/OS 3.1. If that is not possible, install BSDIpatch M300-038. 2. Use the following command when configuring *MySQL*: shell> env CXX=shlicc++ CC=shlicc2 \ ./configure \ --prefix=/usr/local/mysql \ --localstatedir=/var/mysql \ --without-perl \ --with-unix-socket-path=/var/mysql/mysql.sock The following is also known to work: shell> env CC=gcc CXX=gcc CXXFLAGS=-O3 \ ./configure \ --prefix=/usr/local/mysql \ --with-unix-socket-path=/var/mysql/mysql.sock You can change the directory locations if you wish, or just use the defaults by not specifying any locations. 3. If you have problems with performance under heavy load, try using the `--skip-thread-priority' option to `safe_mysqld'! This will run all threads with the same priority; on BSDI 3.1, this gives better performance. (At least until BSDI fixes their thread scheduler). If you get the error `virtual memory exhausted' while compiling, you should try using `ulimit -v 80000' and run `make' again. If this doesn't work and you are using `bash', try switching to `csh' or `sh'; Some BSDI users have reported problems with `bash' and `ulimit'. SCO notes --------- The current port is tested only on a "sco3.2v5.0.4" system. There has also been a lot of progress on a port to "sco 3.2v4.2". 1. For OpenServer 5.0.X You need to use GDS in Skunkware 95 (95q4c). This is necessary because GNU `gcc' 2.7.2 in Skunkware 97 does not have GNU `as'. 2. You need the port of GCC 2.5.? for this product and the Development system. They are required on this version of SCO UNIX. You cannot just use the GCC Dev system. 3. You should get FSU thread package and install this first. This can be found at `http://www.cs.wustl.edu/~schmidt/ACE_wrappers/FSU-threads.tar.gz'. You can also get a precompiled package from `ftp://www.tcx.se/pub/mysql/Downloads/SCO/FSU-threads-3.5c.tar.gz'. 4. FSU pthreads can be compiled with SCO UNIX 4.2 with tcpip. Or OpenServer 3.0 or Open Desktop 3.0 (OS 3.0 ODT 3.0), with the SCO Development System installed using a good port of GCC 2.5.X ODT or OS 3.0 you will need a good port of GCC 2.5.? There are a lot of problems without a good port. The port for this product requires the SCO UNIX Development system. Without it, you are missing the libraries and the linker that is needed. 5. To build FSU pthreads in your system, do the following: 1. Run `./configure' in the `threads/src' directory and select the SCO OpenServer option. This command copies `Makefile.SCO5' to `Makefile'. 2. Run `make'. 3. To install in the default `/usr/include' directory, login as root and `cd' to `thread/src' directory, and run `make install'. 6. Remember to use GNU `make' when making *MySQL*. 7. If you don't start `safe_mysqld' as root, you will probably only get the default 110 open files per process. `mysqld' will write a note about this in the log file. 8. With SCO 3.2V4.2, you must use a FSU-pthreads version 3.5c or newer. The following `configure' command should work: shell> CFLAGS="-D_XOPEN_XPG4" CXX=gcc CXXFLAGS="-D_XOPEN_XPG4" \ ./configure \ --with-debug --prefix=/usr/local/mysql \ --with-named-thread-libs="-lgthreads -lsocket -lgen -lgthreads" \ --with-named-curses-libs="-lcurses" \ --without-perl You may get some problems with some include files. In this case you can find new SCO-specific include files at `ftp://www.tcx.se/pub/mysql/Downloads/SCO/SCO-3.2v4.2-includes.tar.gz'. You should unpack this file in the `include' directory of your *MySQL* source tree. SCO development notes: * *MySQL* should automatically detect FSU-threads and link `mysqld' with `-lgthreads -lsocket -lgthreads'. * The SCO development libraries are reentrant in FSU pthreads. SCO claims that its libraries function are reentrant so they must be reentrant with FSU pthreads. FSU pthreads on OpenServer tries to use the SCO scheme to make reentrant library. * FSU threads (at least the version at `www.tcx.se') comes linked with GNU `malloc'. If you encounter problems with memory usage, make sure that `gmalloc.o' is included in `libgthreads.a' and `libgthreads.so'. * In FSU pthreads, the following system calls are pthreads aware: `read()', `write()', `getmsg()', `connect()', `accept()', `select()' and `wait()'. SCO Unixware 7.0 notes ---------------------- *MySQL* 3.22.13 fixes some portability problems under Unixware so you must use at least this version. We have been able to compile *MySQL* with the following configure line on UnixWare 7.0.1: CC=cc CXX=CC ./configure --prefix=/usr/local/mysql IBM-AIX notes ------------- Automatic detection of `xlC' is missing from Autoconf, so something like this is needed when using the IBM compiler: shell> CC="xlc_r -ma -O3 -qstrict" CXX="xlC_r -ma -O3 -qstrict" \ ./configure If you are using `egcs' to compile *MySQL*, you *MUST* use the `-fno-exceptions' flag, as the exception handling in `egcs' is not thread-safe! (This is tested with `egcs' 1.1). We recommend the following `configure' line with `egcs' and `gcc' on AIX: shell> CXX=gcc CXXFLAGS="-felide-constructors -fno-exceptions -fno-rtti" \ ./configure --prefix=/home/monty --with-debug --with-low-memory If you have problems with signals (*MySQL* dies unexpectedly under high load) you may have found an OS bug with threads and signals. In this case you can tell *MySQL* not to use signals by configuring with: shell> CFLAGS=-DDONT_USE_THR_ALARM CXX=gcc \ CXXFLAGS="-felide-constructors -fno-exceptions -fno-rtti -DDONT_USE_THR_ALARM" \ ./configure --prefix=/home/monty --with-debug --with-low-memory This doesn't affect the performance of *MySQL*, but has the side effect that you can't kill clients that are "sleeping" on a connection with `mysqladmin kill' or `mysqladmin shutdown'. The client will instead die when it issues its next command. HP-UX notes ----------- There are a couple of "small" problems when compiling *MySQL* on HP-UX. We recommend that you use `gcc' instead of the HP-UX native compiler as `gcc' produces better code! `gcc' 2.8.0 can't compile `readline' on HP-UX (an internal compiler error occurs) if you are compiling with `-O6'. On the other hand, MIT-pthreads can't be compiled with the HP-UX compiler, because it can't compile `.S' (assembler) files. We got *MySQL* to compile on HP-UX 10.20 by doing the following: shell> CC=gcc CXX=gcc ./configure --prefix=/usr/local/mysql --with-low-memory shell> cd readline shell> edit Makefile and change -O6 to something lower shell> cd .. shell> make shell> make install shell> scripts/mysql_install_db shell> /usr/local/mysql/bin/safe_mysqld & TcX binaries ============ As a service, TcX provides a set of binary distributions of *MySQL* that are compiled at TcX or at sites where customers kindly have given us access to their machines. These distributions are generated with `scripts/make_binary_distribution' and are configured with the following compilers and options. SunOS 4.1.4 2 sun4c with `gcc' 2.7.2.1 `CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql --disable-shared' SunOS 5.5.1 sun4u with `egcs' 1.0.3a `CC=gcc CFLAGS="-O6 -fomit-frame-pointer" CXX=gcc CXXFLAGS="-O6 -fomit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-low-memory' SunOS 5.6 sun4u with `egcs' 2.90.27 `CC=gcc CFLAGS="-O6 -fomit-frame-pointer" CXX=gcc CXXFLAGS="-O6 -fomit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-low-memory' SunOS 5.6 i86pc with `gcc' 2.8.1 `CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql --with-low-memory' Linux 2.0.33 i386 with `pgcc' 2.90.29 (`egcs' 1.0.3a) `CFLAGS="-O6 -mpentium -mstack-align-double -fomit-frame-pointer" CXX=gcc CXXFLAGS="-O6 -mpentium -mstack-align-double -fomit-frame-pointer -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --enable-assembler --with-mysqld-ldflags=-all-static' SCO 3.2v5.0.4 i386 with `gcc' 2.7-95q4 `CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql' AIX 2 4 with `gcc' 2.7.2.2 `CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql' OSF1 V4.0 564 alpha with `gcc' 2.8.1 `CC=gcc CFLAGS=-O CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql --with-low-memory' IRIX 6.3 IP32 with `gcc' 2.8.0 `CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql' BSDI BSD/OS 3.1 i386 with `gcc' 2.7.2.1 `CC=gcc CXX=gcc CXXFLAGS=-O ./configure --prefix=/usr/local/mysql' BSDI BSD/OS 2.1 i386 with `gcc' 2.7.2 `CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql' Anyone who has more optimal options for any of the configurations listed above can always mail them to us at . RPM distributions prior to *MySQL* 3.22 are user-contributed. Beginning with 3.22, some RPMs are TcX-generated. Win32 notes =========== The *MySQL*-Win32 version has by now proven itself to be very stable. The Win32 version of *MySQL* has the same features as the corresponding Unix version with the following exceptions: *Table cache size limitations* Win32 can handle only a very limited number of open files at the same time (about 255). Because of this, you shouldn't increase the number of open connections or number of cached tables very much on Win32. *Win95 and threads* Win95 leaks about 200 bytes of main memory for each thread creation. Because of this, you shouldn't run `mysqld' for an extended time on Win95 if you do many connections, since each connection in *MySQL* creates a new thread! NT doesn't suffer from this bug. *Blocking read* *MySQL* uses a blocking read for each connection. This means that: * A connection will not be disconnected automatically after 8 hours, as happens with the Unix version of *MySQL*. * If a connection "hangs," it's impossible to break it without killing *MySQL*. * `mysqladmin kill' will not work on a sleeping connection. * `mysqladmin shutdown' can't abort as long as there are sleeping connections. We plan to fix this in the near future. *UDF functions* For the moment, *MySQL*-Win32 does not support user definable functions. *`DROP DATABASE'* You can't drop a database that is in use by some thread. *Killing *MySQL* from the task manager* You can't kill *MySQL* from the task manager or with the shutdown utility in Windows95. You must take it down with `mysqladmin shutdown'. *Case-insensitive names* Filenames are case insensitive on Win32, so database and table names are also case insensitive in *MySQL* for Win32. The only restriction is that database and table names must be given in the same case throughout a given statement. The following query would not work because it refers to a table both as `my_table' and as `MY_TABLE': SELECT * FROM my_table WHERE MY_TABLE.col=1; *The `\' directory character* Pathname components in Win95 are separated by `\', which is also the escape character in *MySQL*. If you are using `LOAD DATA INFILE' or `SELECT ... INTO OUTFILE', you must double the `\' character or use Unix style filenames with `/': SELECT * FROM skr INTO OUTFILE 'C:/tmp/skr.txt'; LOAD DATA INFILE "C:\\tmp\\skr.txt" INTO TABLE skr; *`Can't open named pipe' error* If you use the shareware version of *MySQL*-Win32 on NT with the newests mysql-clients you will get the following error: `error 2017: can't open named pipe to host: . pipe...' This is because the release version of *MySQL* uses named pipes on NT by default. You can avoid this error by using the `--host=localhost' option to the new *MySQL* clients or create a file, `C:\my.cnf', that contains the following information: [client] host = localhost ** If you get the error `Access denied for user: 'some-user@unknown' to database 'mysql'' when accessing a *MySQL* server on the same machine, this means that your *MySQL* can't resolve your host name properly. To fix this you should create a file `\windows\hosts' with the following information: 127.0.0.1 localhost Here are some open issues for anyone who might want to help us with the Win32 release: * When you suspend a laptop running Win95, the `mysqld' daemon doesn't accept new connections when the laptop is resumed. We don't know if this is a problem with Win95, TCP/IP or *MySQL*. * It would also be real nice to be able to kill `mysqld' from the task manager. For the moment, you must use `mysqladmin shutdown'. * When registering `mysqld' as a service with `-install' (on NT) it would be nice if you could also add default options on the command line. For the moment, the workaround is to update the `C:\my.cnf' file instead. * Port `readline' to Win32 for use in the `mysql' command line tool. * GUI versions of the standard *MySQL* clients (`mysql', `mysqlshow', `mysqladmin', and `mysqldump') would be nice. * It would be nice if the "read" and "write" to sockets in `net.c' were interruptible. This would make it possible to kill open threads with `mysqladmin kill' on Win32. * Documentation of which Windows programs work with *MySQL*-Win32/*MyODBC* and what must be done to get them working. * `mysqld' always starts in the "C" locale and not in the default locale. We would like to have `mysqld' use the current locale for the sort order. * Add more options to MysqlManager * Change the communication protocol between the server and client to use Windows internal communication instead of sockets and TCP/IP. * Implement UDF functions with `.DLL's Other Win32-specific issues are described in the `README' file that comes with the *MySQL*-Win32 distribution. Post-installation setup and testing =================================== Once you've installed *MySQL* (from either a binary or source distribution), you need to initialize the grant tables, start the server and make sure that the server works okay. You may also wish to arrange for the server to be started and stopped automatically when your system starts up and shuts down. Normally you install the grant tables and start the server like this: shell> ./scripts/mysql_install_db shell> cd mysql_installation_directory shell> ./bin/safe_mysqld & This is described in detail below: Testing is most easily done from the top-level directory of the *MySQL* distribution. For a binary distribution, this is your installation directory (typically something like `/usr/local/mysql'). For a source distribution, this is the main directory of your *MySQL* source tree. In the commands shown below in this section and in the following subsections, `BINDIR' is the path to the location in which programs like `mysqladmin' and `safe_mysqld' are installed. For a binary distribution, this is the `bin' directory within the distribution. For a source distribution, `BINDIR' is probably `/usr/local/bin', unless you specified an installation directory other than `/usr/local' when you ran `configure'. `EXECDIR' is the location in which the `mysqld' server is installed. For a binary distribution, this is the same as `BINDIR'. For a source distribution, `EXECDIR' is probably `/usr/local/libexec'. 1. If necessary, start the `mysqld' server and set up the initial *MySQL* grant tables containing the privileges that determine how users are allowed to connect to the server. This is normally done with the `mysql_install_db' script. Normally, `mysql_install_db' needs to be run only the first time you install *MySQL*. Therefore, if you are upgrading an existing installation, you can skip this step. `mysql_install_db' is quite safe to use and will not update any tables that already exist, so if you are unsure what to do, you can always run `mysql_install_db'. shell> scripts/mysql_install_db If you don't set up the grant tables, the following error will appear in the log file when you start the server: mysqld: Can't find file: 'host.frm' You might need to run `mysql_install_db' as `root'. However, if you prefer, you can run the *MySQL* server as an unprivileged (non-`root') user, provided that user can read and write files in the database directory. Instructions for running *MySQL* as an unprivileged user are given in *Note Changing *MySQL* user: Changing MySQL user. `mysql_install_db' creates four tables (`user', `db', `host' and `func') in the `mysql' database. A description of the initial privileges is given in *Note Default privileges::. Briefly, the these privileges allow the *MySQL* `root' user to do anything, and allow anybody to create or use databases with a name of `'test'' or starting with `'test_''. If you have problems with `mysql_install_db', see *Note `mysql_install_db': mysql_install_db. There are some alternatives to running the `mysql_install_db' script as is: * You may want to edit `mysql_install_db' before running it, to change the initial privileges that are installed into the grant tables. * If you want to change things in the grant tables after installing them, you can run `mysql_install_db', then use `mysql -u root mysql' to connect to the grant tables as the *MySQL* `root' user and issue SQL statements to modify the grant tables directly. * It is possible to recreate the grant tables completely after they have already been created. You might want to do this if you've already installed the tables but then want to recreate them after editing `mysql_install_db'. For more information about these alternatives, see *Note Default privileges::. 2. Start the *MySQL* server like this: shell> cd mysql_installation_directory shell> bin/safe_mysqld & *Note Starting server:: 3. Verify that the server is running using `mysqladmin'. The following commands provide a simple test to check that the server is up and responding to connections: shell> BINDIR/mysqladmin version shell> BINDIR/mysqladmin variables For example, the output from `mysqladmin version' varies slightly depending on your platform and version of *MySQL*, but should be similar to that shown below: shell> BINDIR/mysqladmin version mysqladmin Ver 6.3 Distrib 3.22.9-beta, for pc-linux-gnu on i686 TCX Datakonsult AB, by Monty Server version 3.22.9-beta Protocol version 10 Connection Localhost via UNIX socket TCP port 3306 UNIX socket /tmp/mysql.sock Uptime: 16 sec Running threads: 1 Questions: 20 Reloads: 2 Open tables: 3 To get a feeling for what else you can do with `BINDIR/mysqladmin', invoke it with the `--help' option. 4. Verify that you can shut down the server: shell> BINDIR/mysqladmin -u root shutdown 5. Verify that you can restart the server. Do this using `safe_mysqld' or by invoking `mysqld' directly. For example: shell> BINDIR/safe_mysqld --log & If `safe_mysqld' fails, try running it from the *MySQL* installation directory (if you are not already there). If that doesn't work, see *Note Starting server::. 6. Run some simple tests to verify that the server is working. The output should be similar to what is shown below: shell> BINDIR/mysqlshow +-----------+ | Databases | +-----------+ | mysql | +-----------+ shell> BINDIR/mysqlshow mysql Database: mysql +--------+ | Tables | +--------+ | db | | host | | user | +--------+ shell> BINDIR/mysql -e "select host,db,user from db" mysql +------+--------+------+ | host | db | user | +------+--------+------+ | % | test | | | % | test_% | | +------+--------+------+ There is also a benchmark suite in `sql-bench' that you can use to compare how *MySQL* performs on different platforms. In the `sql-bench/Results' directory you can find the results from many runs against different databases and platforms. To run all tests, execute these commands: shell> cd sql-bench shell> run-all-tests If you don't have the `sql-bench' directory, you are probably using a RPM for a binary distribution. (Source distribution RPMs include the benchmark directory.) In this case, you must first install the benchmark suite before you can use it. Beginning with *MySQL* 3.22, there are benchmark RPM files named `mysql-bench-VERSION-i386.rpm' that contain benchmark code and data. You can also run the tests in the `tests' subdirectory. For example, to run `auto_increment.tst', do this: shell> BINDIR/mysql -vvf test < ./tests/auto_increment.tst The expected results are shown in the file `./tests/auto_increment.res'. Problems running `mysql_install_db' ----------------------------------- This section lists some of the problems you might encounter when you run `mysql_install_db': *`mysql_install_db' doesn't install the grant tables* You may find that `mysql_install_db' doesn't install the grant tables, but terminates after displaying the following messages: starting mysqld daemon with databases from XXXXXX mysql daemon ended In this case, you should examine the log file very carefully! The log should be located in the directory `XXXXXX' named by the error message, and should indicate why `mysqld' didn't start. If you don't understand what happened, include the log when you post a bug report using `mysqlbug'! *Note Bug reports::. *There is already a `mysqld' daemon running* In this case, you have probably don't have to run `mysql_install_db' at all. You have to run `mysql_install_db' only once, when you install *MySQL* the first time. *Installing a second `mysqld' daemon doesn't work when one daemon is running* This can happen when you already have an existing *MySQL* installation, but want to put a new installation in a different place (e.g., for testing, or perhaps you simply want to run two installations at once). Generally the problem that occurs when you try to run the second server is that it tries to use the same socket and port as the old one. In this case you will get the error message: `Can't start server: Bind on TCP/IP port: Address already in use' or `Can't start server : Bind on unix socket...' You can start the new server with a different socket and port as follows: shell> MYSQL_UNIX_PORT=/tmp/mysqld-new.sock shell> MYSQL_TCP_PORT=3307 shell> export MYSQL_UNIX_PORT MYSQL_TCP_PORT shell> scripts/mysql_install_db shell> bin/safe_mysqld & After this, you should edit your server boot script to start both daemons with different sockets and ports. For example, it could invoke `safe_mysqld' twice, but with different `--socket', `--port' and `--basedir' options for each invocation. *You don't have write access to `/tmp'* If you don't have write access to create a socket file at the default place (in `/tmp') or permission to create temporary files in /tmp, you will get an error when running `mysql_install_db' or when starting/using `mysqld'. You can specify a different socket and temporary directory as follows: shell> MYSQL_UNIX_PORT=/some_tmp_dir/mysqld.sock shell> TMPDIR=/some_tmp_dir/ shell> export MYSQL_UNIX_PORT TMPDIR `some_tmp_dir' should be the path to some directory for which you have write permission. After this you should be able to run `mysql_install_db' and start the server with: shell> scripts/mysql_install_db shell> BINDIR/safe_mysqld & *`mysqld' crashes at once* If you are running RedHat 5.0 with a version of `glibc' older than 2.0.7-5, you should make sure you have installed all `glibc' patches! There is a lot of information about this in the *MySQL* mail archives. *Note Linux::. Links to the mail archives are available at the online *MySQL* documentation page (http://www.tcx.se/doc.html). You can also start `mysqld' manually using the `--skip-grant' option and add the privilege information yourself using `mysql': shell> BINDIR/safe_mysqld --skip-grant & shell> BINDIR/mysql -u root mysql From `mysql', manually execute the SQL commands in `mysql_install_db'. Make sure you run `mysqladmin reload' afterward to tell the server to reload the grant tables. Problems starting the *MySQL* server ------------------------------------ Generally, you start the `mysqld' server in one of three ways: * By invoking `mysql.server'. This script is used primarily at system startup and shutdown, and is described more fully in *Note Automatic start::. * By invoking `safe_mysqld', which tries to determine the proper options for `mysqld' and then runs it with those options. * By invoking `mysqld' directly. Whichever method you use to start the server, if it fails to start up correctly, check the log file to see if you can find out why. Log files are located in the data directory (typically `/usr/local/mysql/data' for a binary distribution, `/usr/local/var' for a source distribution). Look in the data directory for a file with a name of the form `host_name.log', where `host_name' is the name of your server host. Then check the last few lines of that file: shell> tail host_name.log When the `mysqld' daemon starts up, it changes directory to the data directory. This is where it expects to write log files and the pid (process ID) file, and where it expects to find databases. The data directory location is hardwired in when the distribution is compiled. However, if `mysqld' expects to find the data directory somewhere other than where it really is on your system, it will not work properly. If you have problems with incorrect paths, you can find out what options `mysqld' allows and what the default path settings are by invoking `mysqld' with the `--help' option. You can override the defaults by specifying the correct pathnames as command-line arguments to `mysqld'. (These options can be used with `safe_mysqld' as well.) Normally you should need to tell `mysqld' only the base directory under which *MySQL* is installed. You can do this with the `--basedir' option. You can also use `--help' to check the effect of changing path options (note that `--help' *must* be last). For example: shell> EXECDIR/mysqld --basedir=/usr/local --help Once you determine the path settings you want, start the server without the `--help' option. If you get the following error: Can't start server: Bind on TCP/IP port: Address already in use or Can't start server : Bind on unix socket... this means that some other program (or another `mysqld' server) is already using the TCP/IP port or socket `mysqld' tries to use! You should check with `ps' that you don't have another `mysqld' server running. If you can't find another server running, you can try doing `telnet your-host-name tcp-ip-port-number' and press `RETURN' a couple of times. If you don't get a error message like `telnet: Unable to connect to remote host: Connection refused', something is using the TCP/IP port `mysqld' is trying to use. *Note mysql_install_db::, *Note Multiple servers::. The `safe_mysqld' script is written so that it normally is able to start a server that was installed from either a source or a binary version of *MySQL*, even if these install the server in slightly different locations. `safe_mysqld' expects one of these conditions to be true: * The server and databases can be found relative to the directory from which `safe_mysqld' is invoked. `safe_mysqld' looks under its working directory for `bin' and `data' directories (for binary distributions) or for `libexec' and `var' directories (for source distributions). This condition should be met if you execute `safe_mysqld' from your *MySQL* installation directory (for example, `/usr/local/mysql' for a binary distribution). * If the server and databases cannot be found relative to its working directory, `safe_mysqld' attempts to locate them by absolute pathnames. Typical locations are `/usr/local/libexec' and `/usr/local/var'. The actual locations are determined when the distribution was built from which `safe_mysqld' comes. They should be correct if *MySQL* was installed in a standard location. Since `safe_mysqld' will try to find the server and databases relative to its own working directory, you can install a binary distribution of *MySQL* anywhere, as long as you start `safe_mysqld' from the *MySQL* installation directory: shell> cd mysql_installation_directory shell> BINDIR/safe_mysqld & If `safe_mysqld' fails, even when invoked from the *MySQL* installation directory, you can modify it to use the path to `mysqld' and the pathname options that are correct for your system. Note that if you upgrade *MySQL* sometime, your modified version will be overwritten, so you should make a copy of your edited version that you can reinstall. If `mysqld' is currently running, you can find out what path settings it is using by executing this command: shell> mysqladmin variables If `safe_mysqld' starts the server but you can't connect to it, you should make sure you have an entry in `/etc/hosts' that looks like this: 127.0.0.1 localhost This problem occurs only on systems that don't have a working thread library and for which *MySQL* must be configured to use MIT-pthreads. Automatically starting and stopping *MySQL* ------------------------------------------- The `mysql.server' script can be used to start or stop the server, by invoking it with `start' or `stop' arguments: shell> mysql.server stop shell> mysql.server start `mysql.server' can be found in the `share/mysql' directory under the *MySQL* installation directory, or in the `support-files' directory of the *MySQL* source tree. Before `mysql.server' starts the server, it changes directory to the *MySQL* installation directory, then invokes `safe_mysqld'. You might need to edit `mysql.server' if you have a binary distribution that you've installed in a non-standard location. Modify it to `cd' into the proper directory before it runs `safe_mysqld'. You can also modify `mysql.server' to pass other options to `safe_mysqld'. For example, if you want the server to run as some specific user, change the `--user' option in the `safe_mysqld' invocation. (You must run `mysql.server' as the Unix `root' user for this to work.) `mysql.server stop' brings down the server by issuing a `mysqladmin shutdown' command. You should make the script unreadable to anyone but `root' since you will need to put the password for the *MySQL* `root' user in the script. Alternatively, you could edit `mysql.server' to read the server pid file from the data directory to get the server process ID, and kill that process. You can take down the server manually by executing `mysqladmin shutdown' yourself. You might want to add these start and stop commands to the appropriate places in your `/etc/rc*' files when you start using *MySQL* for production applications. Note that if you modify `mysql.server', then if you upgrade *MySQL* sometime, your modified version will be overwritten, so you should make a copy of your edited version that you can reinstall. Option files ------------ *MySQL* 3.22 can read default startup options for the server and for clients from option files. *MySQL* reads default options from the following files on Unix: *Filename* *Purpose* `/etc/my.cnf' Global options `DATADIR/my.cnf' Server-specific options `~/.my.cnf' User-specific options `DATADIR' is the *MySQL* data directory (typically `/usr/local/mysql/data' or `/usr/local/var'). Note that this is the directory that was specified at configuration time, not the one specified with `--datadir' when `mysqld' starts up! (The server looks for option files before it processes any command-line arguments, so `--datadir' has no effect on where the server looks for those files.) *MySQL* reads default options from the following files on Win32: *Filename* *Purpose* `C:\my.cnf' Global options `C:\mysql\data\my.cnf' Server-specific options *MySQL* tries to read option files in the order listed above. If multiple option files exist, an option specified in a file read later overrides the same option specified in a file read earlier. Options specified on the command line override options specified in any option file. Some options can be specified using environment variables. Options specified on the command line or in option files override environment variable values. The following programs support option files: `mysql', `mysqladmin', `mysqld', `mysqldump', `mysqlimport', `isamchk' and `pack_isam'. In option files, you can specify any long option that a program supports! Run the program with `--help' to get a list of available options. An option file can contain lines of the following forms: `#comment' Comment lines starts with `#' or `;'. Empty lines are ignored. `[group]' `group' is the name of the program or group for which you want to set options. After a group line, any `option' or `set-variable' lines apply to the named group, until the end of the option file or another group line is given. `option' This is equivalent to `--option' on the command line. `option=value' This is equivalent to `--option=value' on the command line. `set-variable = variable=value' This is equivalent to `--set-variable variable=value' on the command line. This syntax must be used to set a `mysqld' variable. The `client' group allows you to specify options that apply to all *MySQL* clients (not `mysqld'). This is the perfect group to use to specify the password you use to connect to the server. (But make sure the option file is readable and writable only to yourself.) Note that for options and values, all leading and trailing blanks are automatically deleted. You may use the escape sequences `\b', `\t', `\n', `\r', `\\' and `\s' in your value string (`\s' == blank). Here is a typical global option file: [client] port=3306 socket=/tmp/mysql.sock [mysqld] port=3306 socket=/tmp/mysql.sock set-variable = key_buffer=16M set-variable = max_allowed_packet=1M [mysqldump] quick Here is typical user option file: [client] # The following password will be sent to all standard MySQL clients password=my_password [mysql] no-auto-rehash If you have a source distribution, you will find a sample configuration file named `my-example.cnf' in the `support-files' directory. If you have a binary distribution, look in the `DIR/share/mysql' directory, where `DIR' is the pathname to the *MySQL* installation directory (typically `/usr/local/mysql'). You can copy `my-example.cnf' to your home directory (rename the copy to `.my.cnf') to experiment with. To tell a *MySQL* program not to read any option files, specify `--no-defaults' as the first option on the command line. This *MUST* be the first option or it will have no effect! If you want to check which options are used, you can give the option `--print-defaults' as the first option. Note for developers: Option file handling is implemented simply by processing all matching options (i.e., options in the appropriate group) before any command line arguments. This works nicely for programs that use the last instance of an option that is specified multiple times. If you have an old program that handles multiply-specified options this way but doesn't read option files, you need add only two lines to give it that capability. Check the source code of any of the standard *MySQL* clients to see how to do this. Is there anything special to do when upgrading/downgrading *MySQL*? =================================================================== You can always move the *MySQL* form and data files between different versions on the same architecture as long as you have the same base version of *MySQL*. The current base version is 3. If you change the character set by recompiling *MySQL* (which may also change the sort order), you must run `isamchk -r -q' on all tables. Otherwise your indexes may not be ordered correctly. If you are paranoid and/or afraid of new versions, you can always rename your old `mysqld' to something like `mysqld'-'old-version-number'. If your new `mysqld' then does something unexpected, you can simply shut it down and restart with your old `mysqld'! When you do an upgrade you should also backup your old databases, of course. Sometimes it's good to be a little paranoid! After an upgrade, if you experience problems with recompiled client programs, like `Commands out sync' or unexpected core dumps, you probably have used an old header or library file when compiling your programs. In this case you should check the date for your `mysql.h' file and `libmysql.a' library to verify that they are from the new *MySQL* distribution. If not, please recompile your programs! Upgrading from a 3.21 version to 3.22 ------------------------------------- Nothing that affects compatibility has changed between 3.21 and 3.22. The only pitfall is that new tables that are created with `DATE' type columns will use the new way to store the date. You can't access these new fields from an old version of `mysqld'. After installing `MySQL 3.22' you should start the new server and then run the `mysql_fix_privilege_tables' script. This will add the new privileges that you need to use the `GRANT' command. If you forget this, you will get `Access denied' when you try to use `ALTER TABLE' or `CREATE/DROP INDEX'. If your `MySQL' root user requires a password, you should give this as an argument to `mysql_fix_privilege_tables'. The C API interface to `mysql_real_connect()' has changed. If you have an old client program that calls this function, you must place a `0' for the new `db' argument (or recode the client to send the `db' element for faster connections). Upgrading from a 3.20 version to 3.21 ------------------------------------- If you already have a version older than 3.20.28 running and want to switch to 3.21.x, you need to do the following: You can start the `mysqld' 3.21 server with `safe_mysqld --old-protocol' to use it with clients from the 3.20 distribution. In this case, the new client function `mysql_errno()' will not return any server error, only `CR_UNKNOWN_ERROR', (but it works for client errors) and the server uses the old password() checking rather than the new one. If you are *NOT* using the `--old-protocol' option to `mysqld', you will need to make the following changes: * All client code must be recompiled. If you are using ODBC, you must get the new *MyODBC* 2.x driver. * The script `scripts/add_long_password' must be run to convert the `password' field in the `mysql.user' table to `CHAR(16)'. * All passwords must be reassigned in the `mysql.user' table (to get 62-bit rather than 31-bit passwords). * The table format hasn't changed, so you don't have to convert any tables. *MySQL* 3.20.28 and above can handle the new `user' table format without affecting clients. If you have a *MySQL* version earlier than 3.20.28, passwords will no longer work on it if you convert the `user' table. So to be safe, you should first upgrade to at least 3.20.28 and then upgrade to 3.21.x. The new client code works with a 3.20.x `mysqld' server, so if you experience problems with 3.21.x, you can use the old 3.20.x server without having to recompile the clients again. If you are not using the `--old-protocol' option to `mysqld', old clients will issue the error message: ERROR: Protocol mismatch. Server Version = 10 Client Version = 9 The new Perl `DBI'/`DBD' interface also supports the old `mysqlperl' interface. The only change you have to make if you use `mysqlperl' is to change the arguments to the `connect()' function. The new arguments are: `host', `database', `user', `password' (the `user' and `password' arguments have changed places). The following changes may affect queries in old applications: * `HAVING' must now be specified before any `ORDER BY' clause. * The parameters to `LOCATE()' has been swapped. * There are some new reserved words. The most notable are `DATE', `TIME' and `TIMESTAMP'. Upgrading to another architecture --------------------------------- Currently the *MySQL* data and index files (`*.ISD' and `*.ISM' files) are architecture-dependent and in some case OS-dependent. If you want to move your applications to another machine that has a different architecture/OS than your current machine, you should not try to move a database by simply copying the files to the other machine. You should use `mysqldump' instead. By default, `mysqldump' will create a file full of SQL statements. You can then transfer the file to the other machine and feed it as input to the `mysql' client. Try `mysqldump --help' to see what options are available. If you are moving the data to a newer version of *MySQL*, you should use `mysqldump --opt' with the newer version to get a fast, compact dump. The easiest (although not the fastest) way to move a database between two machines is to run the following commands on the machine on which the database is located: shell> mysqladmin -h 'other hostname' create db_name shell> mysqldump --opt db_name \ | mysql -h 'other hostname' db_name If you want to copy a database from a remote machine over a slow network, you can use: shell> mysqladmin create db_name shell> mysqldump -h 'other hostname' --opt --compress db_name \ | mysql db_name You can also store the result in a file (compressed in this example): shell> mysqldump --quick db_name | gzip > db_name.contents.gz Transfer the file containing the database contents to the target machine and run these commands there: shell> mysqladmin create db_name shell> gunzip < db_name.contents.gz | mysql db_name You can also use `mysqldump' and `mysqlimport' to accomplish the database transfer. For big tables, this is much faster than simply using `mysqldump'. In the commands shown below, `DUMPDIR' represents the full pathname of the directory you use to store the output from `mysqldump'. First, create the directory for the output files and dump the database: shell> mkdir DUMPDIR shell> mysqldump --tab=DUMPDIR db_name Then transfer the files in the `DUMPDIR' directory some corresponding directory on the target machine and load the files into *MySQL* there: shell> mysqladmin create db_name shell> cat DUMPDIR/*.sql | mysql db_name shell> mysqlimport db_name PATH/*.txt Also, don't forget to copy the `mysql' database, since that's where the grant tables (`user', `db', `host') are stored. You may have to run commands as the *MySQL* `root' user on the new machine until you have the `mysql' database in place. After you import the `mysql' database on the new machine, execute `mysqladmin reload' so that the server reloads the grant table information. How standards-compatible is *MySQL*? ************************************ *MySQL* extensions to ANSI SQL92 ================================ *MySQL* includes some extensions that you probably will not find in other SQL databases. Be warned that if you use them, your code will not be portable to other SQL servers. In some cases, you can still write portable code that includes *MySQL* extensions by using comments of the form `/*! ... */'. In this case, *MySQL* will execute the code within the comment. For example: SELECT /*! STRAIGHT_JOIN */ col_name from table1,table2 WHERE ... *MySQL* extensions are listed below: * The field types `MEDIUMINT', `SET', `ENUM' and the different `BLOB' and `TEXT' types. * The field attributes `AUTO_INCREMENT', `BINARY', `UNSIGNED' and `ZEROFILL'. * All string comparisons are case insensitive by default, with sort ordering determined by the current character set (ISO-8859-1 Latin1 by default). If you don't like this, you should declare your columns with the `BINARY' attribute, which causes comparisons to be done according to the ASCII order used on the *MySQL* server host. * *MySQL* maps databases to directories and tables to filenames. This has two implications: - Database names and table names are case sensitive in *MySQL* on operating systems that have case sensitive filenames (like most Unix systems). If you have a problem remembering table names, create everything in lowercase. - You can use standard system commands to backup, rename, move, delete and copy tables. For example, to rename a table, rename the `.ISD', `.ISM' and `.frm' files to which the table corresponds. * In SQL statements, you can access tables from different databases with the `db_name.tbl_name' syntax. Some SQL servers provide the same functionality but call this `User space'. *MySQL* dosen't support tablespaces like in: `create table ralph.my_table...IN my_tablespace'. * `LIKE' is allowed on numeric columns. * Use of `INTO OUTFILE' and `STRAIGHT_JOIN' in a `SELECT' statement. *Note Select::. * `EXPLAIN SELECT' to get a description on how tables are joined. * Use of index names, indexes on a subpart of a field, and use of `INDEX' or `KEY' in a `CREATE TABLE' statement. *Note Create table::. * Use of `CHANGE col_name', `DROP col_name' or `DROP INDEX' in an `ALTER TABLE' statement. *Note Alter table::. * Use of `IGNORE' in an `ALTER TABLE' statement. * Use of multiple `ADD', `ALTER', `DROP' or `CHANGE' clauses in an `ALTER TABLE' statement. * Use of `DROP TABLE' with the keywords `IF EXISTS'. * Use of `DROP TABLE' with more than one table. * Use of `LOAD DATA INFILE'. In many cases, this syntax is compatible with Oracle's `LOAD DATA INFILE'. *Note Load::. * Use of `OPTIMIZE TABLE'. * Strings may be enclosed by either `"' or `'', not just by `''. * Using the escape `\' character. * The `SET OPTION' statement. *Note Set option::. * You don't need to have all columns in the `GROUP BY' part. This gives better performance for some very specific, but quite normal queries. *Note Group by functions::. * To make it easier for a user that comes from different SQL environments *MySQL* supports aliases for many functions. For example, all string functions support both the ANSI SQL and the ODBC syntax. * *MySQL* understands the `||' and `&&' operators to mean logical OR and AND, as in the C programming language. In *MySQL*, `||' and `OR' are synonyms, as are `&&' and `AND'. Because of this nice syntax, *MySQL* doesn't support the ANSI SQL operator `||' for string concatenation; use `CONCAT()' instead. Since `CONCAT()' takes any number of arguments, it's easy to convert use of the `||' operator to *MySQL*. * To support use of *MySQL*-specific keywords as `STRAIGHT_JOIN' in SQL code that should be portable, you can embed them in a `/* */' comment that starts with a `'!''. In this case *MySQL* will parse the comment as it would any other *MySQL* statement, but other SQL servers will ignore the extensions. For example: SELECT /*! STRAIGHT_JOIN */ * from table1,table2 WHERE ... * Use of any of the following functions or commands: * `CREATE DATABASE' or `DROP DATABASE'. *Note Create database::. * `%' instead of `MOD()'. `%' is supported for C programmers and for compatibility with PostgreSQL. * `=', `<>', `<=' ,`<', `>=',`>', `<<', `>>', `AND', `OR' or `LIKE' in a column statement. * `LAST_INSERT_ID()'. *Note `mysql_insert_id()': mysql_insert_id. * `REGEXP' or `NOT REGEXP'. * `CONCAT()' or `CHAR()' with one or more than two arguments. In *MySQL* these functions can take any number of arguments. * `BIT_COUNT()', `ELT()', `FROM_DAYS()', `FORMAT()', `IF()', `PASSWORD()', `ENCRYPT()', `PERIOD_ADD()', `PERIOD_DIFF()', `TO_DAYS()', or `WEEKDAY()'. * Use of `TRIM()' to trim substrings. ANSI SQL only supports removal of single characters. * The `STD()', `BIT_OR()' and `BIT_AND()' group functions. * Use of `REPLACE' instead of `DELETE' + `INSERT'. *Note Replace::. * The `FLUSH flush_option' command. Functionality missing from *MySQL* ================================== The following functionality is missing in the current version of *MySQL*. For the priority of new extensions, you should consult the *MySQL* TODO list (http://www.tcx.se/Manual_split/manual_Todo.html). That is the latest version of the TODO list in this manual. *Note TODO::. Sub-selects ----------- The following will not work in *MySQL*: SELECT * FROM table1 WHERE id IN (SELECT id FROM table2); *MySQL* only supports `INSERT ... SELECT ...' and `REPLACE ... SELECT ...' Independent sub-selects will be probably be available in 3.23.0. You can now use the function `IN()' in other contexts, however. `SELECT INTO TABLE' ------------------- *MySQL* doesn't yet support `SELECT ... INTO TABLE ...'. Currently, *MySQL* only supports `SELECT ... INTO OUTFILE ...', which is basically the same thing. Transactions ------------ Transactions are not supported. *MySQL* shortly will support atomic operations, which are like transactions without rollback. With atomic operations, you can execute a group of insert/select/whatever commands and be guaranteed that no other thread will interfere. In this context, you won't usually need rollback. Currently, you can prevent interference from other threads with the help of the `LOCK TABLES' and `UNLOCK TABLES' commands. *Note Lock tables::. Stored procedures and triggers ------------------------------ A stored procedure is a set of SQL commands that can be compiled and stored in the server. Once this has been done, clients don't need to keep reissuing the entire query but can refer to the stored procedure. This provides more speed because the query has to be parsed only once and less data need be sent between the server and the client. You can also raise the conceptual level by having libraries of functions in the server. A trigger is a stored procedure that is invoked when a particlar event occurs. For example, you can install a stored procedure that is triggered each time a record is deleted from a transaction table and that automatically deletes the corresponding customer from a customer table when all his transactions are deleted. The planned update language will be able to handle stored procedures, but without triggers. Triggers usually slow down everything, even queries for which they are not needed. To see when *MySQL* might get stored procedures, see *Note TODO::. Foreign Keys ------------ Note that foreign keys in SQL are not used to join tables, but are used mostly for checking referential integrity. If you want to get results from multiple tables from a `SELECT' statement, you do this by joining tables! SELECT * from table1,table2 where table1.id = table2.id *Note Join::. The `FOREIGN KEY' syntax in *MySQL* exists only for compatibility with other SQL vendors' `CREATE TABLE' commands; it doesn't do anything. The `FOREIGN KEY' syntax without `ON DELETE ...' is mostly used for documentation purposes. Some ODBC applications may use this to produce automatic `WHERE' clauses, but this is usually easy to override. `FOREIGN KEY' is sometimes used as a constraint check, but this check is unnecessary in practice if rows are inserted into the tables in the right order. *MySQL* only supports these clauses because some applications require them to exist (regardless of whether or not they work!). In *MySQL*, you can work around the problem of `ON DELETE ...' not being implemented by adding the appropriate `DELETE' statement to an application when you delete records from a table that has a foreign key. In practice this is as quick (in some cases quicker) and much more portable than using foreign keys. In the near future we will extend the `FOREIGN KEY' implementation so that at least the information will be saved and may be retrieved by `mysqldump' and ODBC. Reasons NOT to use foreign keys ............................... There are so many problems with `FOREIGN KEY's that we don't know where to start: * Foreign keys make life very complicated, because the foreign key definitions must be stored in a database and implementing them would destroy the whole "nice approach" of using files that can be moved, copied and removed. * The speed impact is terrible fore `INSERT' and `UPDATE' statements, and in this case almost all `FOREIGN KEY' checks are useless because one usually inserts records in the right tables in the right order. * There is also a need to hold locks on many more tables when updating one table, because the side effects can cascade through the entire database. It's MUCH faster to delete records from one table first and subsequently delete them from the other tables. * You can no longer restore a table by doing a full delete from the table and then restoring all records (from a new source or from a backup). * If you have foreign keys you can't dump and restore tables unless you do so in a very specific order. * It's very easy to do "allowed" circular definitions that make the tables impossible to recreate each table with a single create statement, even if the definition works and is usable. The only nice aspect of foreign key is that it gives ODBC and some other client programs the ability to see how a table is connected and use this to show connection diagrams and to help building applicatons. *MySQL* will soon store `FOREIGN KEY' definitions so that a client can ask for and receive an answer how the original connection was made. The current `.frm' file format does not have any place for it. Views ----- *MySQL* doesn't support views, but this is on the TODO. `--' as the start of a comment ------------------------------ Some other SQL databases use `--' to start comments. *MySQL* has `#' as the start comment character, even if the `mysql' command line tool removes all lines that start with `--'. You can also use the C comment style `/* this is a comment */' with *MySQL*. *Note Comments::. *MySQL* will not support `--'; this degenerate comment style has caused many problems with automatically-generated SQL queries that have used something like the following code, where we automatically insert the value of the payment for `!payment!': UPDATE tbl_name SET credit=credit-!payment! What do you think will happen when the value of `payment' is negative? Because `1--1' is legal in SQL, we think it is terrible that `--' means start comment. If you have a SQL program in a text file that contains `--' comments you should use: shell> replace " --" " #" < text-file-with-funny-comments.sql \ | mysql database instead of the normal: shell> mysql database < text-file-with-funny-comments.sql You can also change the `--' comments to `#' comments in the command file: shell> replace " --" " #" -- text-file-with-funny-comments.sql Change them back with this command: shell> replace " #" " --" -- text-file-with-funny-comments.sql What standards does *MySQL* follow? =================================== Entry level SQL92. ODBC level 0-2. Limitations of `BLOB' and `TEXT' types ====================================== If you want to use `GROUP BY' or `ORDER BY' on a `BLOB' or `TEXT' field, you must make the field into a fixed-length object. The standard way to do this is with the `SUBSTRING' function. For example: mysql> select comment from tbl_name order by SUBSTRING(comment,20); If you don't do this, only the first `max_sort_length' bytes (default=1024) are considered when sorting. `BLOB' and `TEXT' cannot have `DEFAULT' values and will also always be `NULL' columns. How to cope without `COMMIT'-`ROLLBACK' ======================================= *MySQL* doesn't support `COMMIT'-`ROLLBACK.' The problem is that handling `COMMIT'-`ROLLBACK' efficiently would require a completely different table layout than *MySQL* uses today. *MySQL* would also need extra threads that do automatic cleanups on the tables and the disk usage would be much higher. This would make *MySQL* about 2-4 times slower than it is today. *MySQL* is much faster than almost all other SQL databases (typically at least 2-3 times faster). One of the reasons for this is the lack of `COMMIT'-`ROLLBACK'. For the moment, we are much more for implementing the SQL server language (something like stored procedures). With this you would very seldom really need `COMMIT'-`ROLLBACK.' This would also give much better performance. Loops that need transactions normally can be coded with the help of `LOCK TABLES', and you don't need cursors when you can update records on the fly. We have transactions and cursors on the TODO but not quite prioritized. If we implement these, it will be as an option to `CREATE TABLE'. That means that `COMMIT'-`ROLLBACK' will only work on those tables and only those tables will be slower. We at TcX have a greater need for a real fast database than a 100% general database. Whenever we find a way to implement these features without any speed loss, we will probably do it. For the moment, there are many more important things to do. Check the TODO for how we prioritize things at the moment. Customers with higher levels of support can alter this, so things may be reprioritized. The current problem is actually `ROLLBACK'. Without `ROLLBACK', you can do any kind of `COMMIT' action with `LOCK TABLES'. To support `ROLLBACK', *MySQL* would have to be changed to store all old records that were updated and revert everything back to the starting point if `ROLLBACK' was issued. For simple cases, this isn't that hard to do (the current `isamlog' could be used for this purpose), but it would be much more difficult to implement `ROLLBACK' for `ALTER/DROP/CREATE TABLE'. To avoid using `ROLLBACK', you can use the following strategy: 1. Use `LOCK TABLES ...' to lock all the tables you want to access. 2. Test conditions. 3. Update if everything is okay. 4. `UNLOCK TABLES' This is usually a much faster method than using transactions with possible `ROLLBACK's, although not always. The only situation this solution doesn't handle is when someone kills the threads in the middle of an update. In this case, all locks will be released but some of the updates may not have been executed. You can also use functions to update records in a single operation. You can get a very efficient application by using the following techniques: * Modify fields relative to their current value * Update only those fields that actually have changed For example, when we are doing updates on some customer information, we update only the customer data that have changed and test only that none of the changed data, or data that depend on the changed data, have changed compared to the original row. The test for changed data is done with the `WHERE' clause in the `UPDATE' statement. If the record wasn't updated, we give the client a message: "Some of the data you have changed have been changed by another user". Then we show the old row versus the new row in a window, so the user can decide which version of the customer record he should use. This gives us something that is similar to "column locking" but is actually even better, because we only update some of the columns with values that are relative to their current values. This means that typical `UPDATE' statements look something like these: UPDATE tablename SET pay_back=pay_back+'relative change'; UPDATE customer SET customer_date='current_date', address='new address', phone='new phone', money_he_owes_us=money_he_owes_us+'new_money' WHERE customer_id=id AND address='old address' AND phone='old phone'; As you can see, this is very efficient and works even if another client has changed the values in the `pay_back' or `money_he_owes_us' columns. In many cases, users have wanted `ROLLBACK' and/or `LOCK TABLES' to manage unique identifiers for some tables. This can be handled much more efficiently by using an `AUTO_INCREMENT' column and either the SQL `LAST_INSERT_ID()' function or the C API function `mysql_insert_id()'. *Note `mysql_insert_id()': mysql_insert_id. At TcX, we have never had any need for row-level locking because we have always been able to code around it. Some cases really need row locking, but they are very few. If you want row-level locking, you can use a flag column in the table and do something like this: UPDATE tbl_name SET row_flag=1 WHERE id=ID; *MySQL* returns 1 for the number of affected rows if the row was found and `row_flag' wasn't already 1 in the original row. The *MySQL* access privilege system *********************************** *MySQL* has an advanced but non-standard security/privilege system. This section describes how it works. What the privilege system does ============================== The primary function of the *MySQL* privilege system is to associate a user name on a host with *select*, *insert*, *update* and *delete* privileges on a database. Additional functionality includes the ability to have an anonymous user and to grant privileges for *MySQL*-specific functions such as `LOAD DATA INFILE' and administrative operations. Please note that user names, as used by *MySQL* for authentication purposes, have nothing to do with Unix user names (login names) or Windows user names. Most *MySQL* clients try to log in using the current Unix user name as the *MySQL* user name, but that is for convenience only. Client programs allow a different name to be specified with the `-u' or `--user' options. This means that you can't make a database secure in any way unless all *MySQL* user names have passwords. Anyone may attempt to connect to the server using any name, and they will succeed if you don't have a password for each name. *MySQL* user names can be up to 16 characters long, whereas Unix user names typically are limited to 8 characters. *MySQL* passwords have nothing to do with Unix passwords, either. There is no necessary connection between the password you use to log in on a Unix machine and the password you use to access a database on that machine. *MySQL* also encrypts passwords using a different algorithm than the one used during the Unix login process. Connecting to the *MySQL* server ================================ *MySQL* client programs generally require that you specify connection parameters: the host you want to connect to, your user name and your password. For example, the `mysql' client can be started like this (optional arguments are enclosed between `[' and `]'): shell> mysql [-h host_name] [-u user_name] [-pyour_pass] Note that there is no space between `-p' and the password following it. Alternate forms of the `-h', `-u' and `-p' options are `--host=host_name', `--user=user_name' and `--password=your_pass'. `mysql' uses default values for connection parameters that are missing from the command line. The default hostname is `localhost' and the default user name is your Unix login name. (No password is supplied if `-p' is missing.) Thus, for a Unix user `joe', the following commands are equivalent: shell> mysql -h localhost -u joe shell> mysql -h localhost shell> mysql -u joe shell> mysql Other *MySQL* clients behave similarly. On Unix systems, you can specify different default values to be used when you make a connection, so that you need not enter them on the command line each time you invoke a client program: * You can specify connection parameters in the `[client]' section of the `.my.cnf' configuration file in your home directory. The relevant section of the file might look like this: [client] host=host_name user=user_name password=your_pass *Note Option files::. * You can specify connection parameters using environment values. The host can be specified using `MYSQL_HOST'. The *MySQL* user name can be specified using `USER', `LOGNAME' or `LOGIN' (although these variables might already be set to your Unix login name, and it may be wise not to change them). The password can be specified using `MYSQL_PWD' (but this is insecure; see next section). If connection parameters are specified in multiple ways, values specified on the command line override values specified in configuration files and environment variables, and values in configuration files override values in environment variables. Keeping your password secure ---------------------------- It is inadvisable to specify your password in a way that exposes it to discovery by other users. The methods you can use to specify your password when you run client programs are listed below, along with an assessment of the risks of each method: * Use a `-pyour_pass' or `--password=your_pass' option on the command line. This is convenient but insecure, since your password becomes visible to system status programs (such as `ps') that may be invoked by other users to display command lines. (*MySQL* clients typically overwrite the command line argument with zeroes during their initialization sequence, but there is still a brief interval during which the value is visible.) * Use a `-p' or `--password' option (with no `your_pass' value specified). In this case, the client program solicits the password from the terminal: shell> mysql -u user_name -p Enter password: ******** The client echoes `*' characters to the terminal as you enter your password so that onlookers cannot see it. It is more secure to enter your password this way than to specify it on the command line because it is not visible to other users. However, this method of entering a password is unsuitable if you want to invoke a client from a script that runs non-interactively. * Store your password in a configuration file. For example, you can list your password in the `[client]' section of the `.my.cnf' file in your home directory: [client] password=your_pass If you store your password in `.my.cnf', the file should not be group or world readable or writable. Make sure the file's access mode is `400' or `600'. * You can store your password in the `MYSQL_PWD' environment variable, but this method must be considered extremely insecure and should not be used. Some versions of `ps' include an option to display the environment of running processes; your password will be in plain sight for all to see if you set `MYSQL_PWD'. Even on systems without such a version of `ps', it is unwise to assume there is no other method to observe process environments. All in all, the safest methods are probably to have the client program prompt for the password or to specify the password in a properly-protected `.my.cnf' file. Privileges provided by *MySQL* ============================== Privilege information is stored in the `user', `db', `host', `tables_priv' and `columns_priv' tables in the `mysql' database (that is, in the database named `mysql'). The *MySQL* server reads the contents of these tables when it starts up and under the circumstances indicated in *Note Privilege changes::. The names used in this manual to refer to the privileges provided by *MySQL* are shown below, along with the table column name associated with each privilege in the grant tables and the context in which the privilege applies: *Privilege* *Column* *Context* *select* `Select_priv' tables *insert* `Insert_priv' tables *update* `Update_priv' tables *delete* `Delete_priv' tables *index* `Index_priv' tables *alter* `Alter_priv' tables *create* `Create_priv' databases, tables or indexes *drop* `Drop_priv' databases or tables *grant* `Grant_priv' databases or tables *reload* `Reload_priv' server administration *shutdown* `Shutdown_priv' server administration *process* `Process_priv' server administration *file* `File_priv' file access on server The *select*, *insert*, *update* and *delete* privileges allow you to perform operations on rows in existing tables in a database. `SELECT' statements require the *select* privilege only if they actually retrieve rows from a table. You can execute certain `SELECT' statements even without permission to access any of the databases on the server. For example, you could use the `mysql' client as a simple calculator: mysql> SELECT 1+1; mysql> SELECT PI()*2; The *index* privilege allows you to create or drop (remove) indexes. The *alter* privilege allows you to use `ALTER TABLE'. The *create* and *drop* privileges allow you to create new databases and tables, or to drop (remove) existing databases and tables. Note that if you grant the *drop* privilege for the `mysql' database to a user, that user can drop the database in which the *MySQL* access privileges are stored! The *grant* privilege allows you to give to other users those privileges you yourself possess. The *file* privilege gives you permission to read and write files on the server using the `LOAD DATA INFILE' and `SELECT ... INTO OUTFILE' statements. Any user to whom this privilege is granted can read or write any file that the *MySQL* server can read or write. The remaining privileges are used for administrative operations, which are performed using the `mysqladmin' program. The table below shows which `mysqladmin' commands each administrative privilege allows you to execute: *Privilege* *Commands permitted to privilege holders* *reload* `reload', `refresh', `flush-privileges', `flush-hosts', `flush-logs', `flush-tables' *shutdown* `shutdown' *process* `processlist', `kill' The `reload' command tells the server to reread the grant tables. The `refresh' command flushes all tables and opens and closes the log files. `flush-privileges' is a synonym for `reload'. The other `flush-*' commands perform functions similar to `refresh' but are more limited in scope, and may be preferable in some instances. For example, if you want to flush just the log files, `flush-logs' is a better choice than `refresh'. The `shutdown' command shuts down the server. The `processlist' command displays information about the threads executing within the server. The `kill' command kills server threads. You can always display or kill your own threads, but you need the *process* privilege to display or kill threads initiated by other users. Certain privileges should be granted sparingly: * The *grant* privilege allows users to give away their privileges to other users. Two users with different privileges and with the *grant* privilege are able to combine privileges. * The *file* privilege can be abused to read any world-readable file on the server into a database table, the contents of which can then be accessed using `SELECT'. * The *shutdown* privilege can be abused to deny service to other users entirely. * The *process* privilege can be used to view the plain text of currently executing queries, including queries that set or change passwords. * Privileges on the `mysql' database can be used to change passwords and other access privilege information. (Even though passwords are stored encrypted, a malicious user can, with sufficient privileges, replace a password with a different one.) There are some things that you cannot do with the *MySQL* privilege system: * You cannot explicitly specify that a given user should be denied access. That is, you cannot explicitly match a user and then refuse the connection. * You cannot specify that a user has privileges to create or drop tables in a database but not to create or drop the database itself. How the privilege system works ============================== The *MySQL* privilege system ensures that all users may do exactly the things that they are supposed to be allowed to do. When you connect to a *MySQL* server, your identity is determined by *the host from which you connect* and *the user name you specify*. The system grants privileges according to your identity and *what you want to do*. *MySQL* considers both your hostname and user name in identifying you because there is little reason to assume that a given user name belongs to the same person everywhere on the Internet. For example, the user `bill' who connects from `whitehouse.gov' need not be the same person as the user `bill' who connects from `microsoft.com'. *MySQL* handles this by allowing you to distinguish users on different hosts that happen to have the same name: you can grant `bill' one set of privileges for connections from `whitehouse.gov', and a different set of privileges for connections from `microsoft.com'. *MySQL* access control involves two stages: * Stage 1: The server checks whether or not you are even allowed to connect. * Stage 2 (assuming the server lets you connect): The server checks each request you issue to see whether or not you have sufficient privileges to perform it. For example, if you try to select rows from a table in a database or drop a table from the database, the server makes sure you have the *select* privilege for the table or the *drop* privilege for the database. The server uses the `user', `db' and `host' tables in the `mysql' database at both stages of access control. The fields in these grant tables are shown below: *Table name* `user' `db' `host' *Scope `Host' `Host' `Host' fields* `User' `Db' `Db' `Password' `User' *Privilege `Select_priv' `Select_priv' `Select_priv' fields* `Insert_priv' `Insert_priv' `Insert_priv' `Update_priv' `Update_priv' `Update_priv' `Delete_priv' `Delete_priv' `Delete_priv' `Index_priv' `Index_priv' `Index_priv' `Alter_priv' `Alter_priv' `Alter_priv' `Create_priv' `Create_priv' `Create_priv' `Drop_priv' `Drop_priv' `Drop_priv' `Grant_priv' `Grant_priv' `Grant_priv' `Reload_priv' `Shutdown_priv' `Process_priv' `File_priv' For the second stage of access control (request verification), the server may, if the request involves tables, additionally consult the `tables_priv' and `columns_priv' tables. The fields in these tables are shown below: *Table name* `tables_priv' `columns_priv' *Scope `Host' `Host' fields* `Db' `Db' `User' `User' `Table_name' `Table_name' `Column_name' *Privilege `Table_priv' `Type' fields* `Column_priv' *Other `Timestamp' `Timestamp' fields* `Grantor' Each grant table contains scope fields and privilege fields. Scope fields determine the scope of each entry in the tables, i.e., the context in which the entry applies. For example, a `user' table entry with `Host' and `User' values of `'thomas.loc.gov'' and `'bob'' would be used for authenticating connections made to the server by `bob' from the host `thomas.loc.gov'. Similarly, a `db' table entry with `Host', `User' and `Db' fields of `'thomas.loc.gov'', `'bob'' and `'reports'' would be used when `bob' connects from the host `thomas.loc.gov' to access the `reports' database. The `tables_priv' and `columns_priv' tables contain scope fields indicating tables or table/column combinations to which each entry applies. For access-checking purposes, comparisons of `Host' values are case insensitive. `User', `Password', `Db' and `Table_name' values are case sensitive. `Column_name' values are case insensitive in *MySQL* 3.22.12 and up (but case sensitive in 3.22.11). Privilege fields indicate the privileges granted by a table entry, that is, what operations can be performed. The server combines the information in the various grant tables to form a complete description of a user's privileges. The rules used to do this are described in *Note Request access::. Scope fields are strings, declared as shown below; the default value for each is the empty string: *Field *Type* name* `Host' `CHAR(60)' `User' `CHAR(16)' `Password' `CHAR(16)' `Db' `CHAR(64)' (`CHAR(60)' for the `tables_priv' and `columns_priv' tables) In the `user', `db' and `host' tables, all privilege fields are declared as `ENUM('N','Y')' -- each can have a value of `'N'' or `'Y'', and the default value is `'N''. In the `tables_priv' and `columns_priv' tables, the privilege fields are declared as `SET' fields: *Table name* *Field name* *Possible set elements* `tables_priv' `Table_priv' `'Select', 'Insert', 'Update', 'Delete', 'Create', 'Drop', 'Grant', 'References', 'Index', 'Alter'' `tables_priv' `Column_priv' `'Select', 'Insert', 'Update', 'References'' `columns_priv' `Type' `'Select', 'Insert', 'Update', 'References'' Briefly, the server uses the grant tables like this: * The `user' table scope fields determine whether to allow or reject incoming connections. For allowed connections, the privilege fields indicate the user's global (superuser) privileges. * The `db' and `host' tables are used together: - The `db' table scope fields determine which users can access which databases from which hosts. The privilege fields determine which operations are allowed. - The `host' table is used as an extension of the `db' table when you want a given `db' table entry to apply to several hosts. For example, if you want a user to be able to use a database from several hosts in your network, leave the `Host' value empty in the user's `db' table entry, then populate the `host' table with an entry for each of those hosts. This mechanism is described more detail in *Note Request access::. * The `tables_priv' and `columns_priv' tables are similar to the `db' table, but are more fine-grained: they apply at the table and column level rather than at the database level. Note that administrative privileges (*reload*, *shutdown*, etc.) are specified only in the `user' table. This is because administrative operations are operations on the server itself and are not database-specific, so there is no reason to list such privileges in the other grant tables. In fact, only the `user' table need be consulted to determine whether or not you can perform an administrative operation. The *file* privilege is specified only in the `user' table, too. It is not an administrative privilege as such, but your ability to read or write files on the server host is independent of the database you are accessing. The `mysqld' server reads the contents of the grant tables once, when it starts up. Changes to the grant tables take effect as indicated in *Note Privilege changes::. When you modify the contents of the grant tables, it is a good idea to make sure that your changes set up privileges the way you want. A useful diagnostic tool is the `mysqlaccess' script, which Yves Carlier has provided for the *MySQL* distribution. Invoke `mysqlaccess' with the `--help' option to find out how it works. Also, see *Note Access denied:: and *Note Security::. Note that `mysqlaccess' checks access using only the `user', `db' and `host' tables. It does not check table- or column-level privileges. Access control, stage 1: Connection verification ================================================ When you attempt to connect to a *MySQL* server, the server accepts or rejects the connection based on your identity and whether or not you can verify your identity by supplying the correct password. If not, the server completely denies access to you. Otherwise, the server accepts the connection, then enters stage 2 and waits for requests. Your identity is based on two pieces of information: * The host from which you connect * Your *MySQL* user name Identity checking is performed using the three `user' table scope fields (`Host', `User' and `Password'). The server accepts the connection only if a `user' table entry matches your hostname and user name, and you supply the correct password. You can specify `user' table scope field values as follows: * A `Host' value may be a hostname or an IP number, or `'localhost'' to indicate the local host, * You can use the wildcard characters `%' and `_' in the `Host' field. * A `Host' value of `'%'' matches any hostname. A blank `Host' value is equivalent to `'%''. Note that these values match *any host that can create a connection to your server!* * Wildcard characters are not allowed in the `User' field, but you can specify a blank value, which matches any name. If the matching entry for an incoming connection has a blank user name, the user is considered to be the anonymous user, the user with no name), rather than the name that the client actually specified. This means that all further access checking for the duration of the connection is done using a blank user name. * The `Password' field can be blank. This does not mean that any password matches, it means the user must connect without specifying a password. The table below shows some examples of how various combinations of `Host' and `User' values in `user' table entries apply to incoming connections: `Host' *value* `User' *Connections matched by entry* *value* `'thomas.loc.gov'' `'fred'' `fred', connecting from `thomas.loc.gov' `'thomas.loc.gov'' `''' Any user, connecting from `thomas.loc.gov' `'%'' `'fred'' `fred', connecting from any host `'%'' `''' Any user, connecting from any host `'%.loc.gov'' `'fred'' `fred', connecting from any host in the `loc.gov' domain `'x.y.%'' `'fred'' `fred', connecting from `x.y.net', `x.y.com', `x.y.edu', etc. (this is probably not useful) `'144.155.166.177''`'fred'' `fred', connecting from the host with IP address `144.155.166.177' `'144.155.166.%'' `'fred'' `fred', connecting from any host in the `144.155.166' class C subnet Since you can use IP wildcard values in the `Host' field (e.g., `'144.155.166.%'' to match every host on a subnet), there is the possibility that someone might try to exploit this capability by naming a host `144.155.166.somewhere.com'. To foil such attempts, *MySQL* disallows matching on hostnames that start with digits and a dot. Thus, if you have a host named something like `1.2.foo.com', its name will never match the `Host' column of the grant tables. Only an IP number can match an IP wildcard value. How does the server choose which `user' table entry to use if more than one matches? This question is resolved by the way the `user' table is sorted, which is done at server startup time. Suppose the `user' table looks like this: +-----------+----------+- | Host | User | ... +-----------+----------+- | % | root | ... | % | jeffrey | ... | localhost | root | ... | localhost | | ... +-----------+----------+- When the server reads in the table, it orders the entries with the most-specific `Host' values first (`'%'' in the `Host' column means "any host" and is least specific). Entries with the same `Host' value are ordered with the most-specific `User' values first (a blank `User' value means "any user" and is least specific). As a result, the sorted `user' table looks like this: +-----------+----------+- | Host | User | ... +-----------+----------+- | localhost | root | ... | localhost | | ... | % | jeffrey | ... | % | root | ... +-----------+----------+- The matching algorithm looks through the sorted entries and uses the first match found. For a connection from `localhost' by `jeffrey', the entries with `'localhost'' in the `Host' column match first. Of those, the entry with the blank user name matches both the connecting hostname and user name. (The `'%'/'jeffrey'' entry would have matched, too, but it is not the first match in the table.) Here is another example. Suppose the `user' table looks like this: +----------------+----------+- | Host | User | ... +----------------+----------+- | % | jeffrey | ... | thomas.loc.gov | | ... +----------------+----------+- The sorted table looks like this: +----------------+----------+- | Host | User | ... +----------------+----------+- | thomas.loc.gov | | ... | % | jeffrey | ... +----------------+----------+- A connection from `thomas.loc.gov' by `jeffrey' is matched by the first entry, whereas a connection from `whitehouse.gov' by `jeffrey' is matched by the second. If you have problems connecting to the server, print out the `user' table and sort it by hand to see where the first match is being made. Access control, stage 2: Request verification ============================================= Once you establish a connection, the server enters stage 2. For each request that comes in on the connection, the server checks whether you have sufficient privileges for it, based on the type of operation you wish to perform. This is where the privilege fields in the grant tables come into play. These privileges can come from any of the `user', `db', `host', `tables_priv' or `columns_priv' tables. The grant tables are manipulated with `GRANT' and `REVOKE' commands. *Note `GRANT': Grant. (You may find it helpful to refer to the table shown earlier that lists the fields present in each of the grant tables; see *Note Privileges::.) The `user' table grants privileges that are assigned to you on a global basis and that apply no matter what the current database is. For example, if the `user' table grants you the *delete* privilege, you can delete rows from any database on the server host! In other words, `user' table privileges are superuser privileges and it is wise to grant privileges in the `user' table only to superusers (such as server or database administrators). For other users, you should leave the privileges in the `user' table set to `'N'' and grant privileges on a database-specific basis only, using the `db' and `host' tables. The `db' and `host' tables grant database-specific privileges. The wildcard characters `%' and `_' can be used in the `Host' and `Db' fields of each table and blank values are allowed in any of the scope fields. A `'%'' `Host' value means "any host." A blank `Host' value in the `db' table means "consult the `host' table for further information." A `'%'' or blank `Db' value in the `host' table means or "any database." A blank `User' value matches the anonymous user. The `db' and `host' tables are read in and sorted when the server starts up (at the same time that it reads the `user' table). The `db' table is sorted on the `Host', `Db' and `User' scope fields, and the `host' table is sorted on the `Host' and `Db' scope fields. As with the `user' table, sorting puts the most-specific values first and least-specific values last, and when the server looks for matching entries, it uses the first match that it finds. The `tables_priv' and `columns_priv' tables grant table- and column-specific privileges. The same wildcards are allowed in the `Host' field as for the `Host' field in the `db' and `host' tables, but the `Db', `Table_name' and `Column_name' fields cannot contain wildcards or be blank. The `tables_priv' and `columns_priv' tables are sorted similarly to the `db' table, although since only the `Host' table may contain wildcards, the sorting is simpler. The request verification process is described below. If you are familiar with the access-checking source code, you will notice that the description here differs slightly from the algorithm used in the code. The description is equivalent to what the code actually does; it differs only to make the explanation simpler. For administrative requests (*shutdown*, *reload*, etc.), the server checks only the `user' table entry, since that is the only table that specifies administrative privileges. Access is granted if the entry allows the requested operation and denied otherwise. For example, if you want to execute `mysqladmin shutdown' but your `user' table entry doesn't grant the *shutdown* privilege to you, access is denied without even checking the `db' or `host' tables (there is no need to do so, because they contain no `Shutdown_priv' column). For database-related requests (*insert*, *update*, etc.), the server first checks the user's global (superuser) privileges by looking in the `user' table entry. If the entry allows the requested operation, access is granted. If the global privileges in the `user' table are insufficient, the server determines the user's database-specific privileges by checking the `db' and `host' tables: 1. The server looks in the `db' table for a match on the `Host', `Db' and `User' fields. `Host' and `User' are matched to the connecting user's hostname and *MySQL* user name. The `Db' field is matched to the database the user wants to access. If there is no entry for the `Host' and `User', access is denied. 2. If there is a matching `db' table entry and its `Host' field is not blank, that entry defines the user's database-specific privileges. 3. If the matching `db' table entry's `Host' field is blank, it signifies that the `host' table enumerates which hosts should be allowed access to the database. In this case, a further lookup is done in the `host' table to find a match on the `Host' and `Db' fields. If no `host' table entry matches, access is denied. If there is a match, the user's database-specific privileges are computed as the intersection of the privileges in the `db' and `host' table entries, i.e., the privileges that are `'Y'' in both entries. (This way you can grant general privileges in the `db' table entry and then selectively restrict them on a host-by-host basis using the `host' table entries.) After determining the database-specific privileges granted by the `db' and `host' table entries, the server adds them to the global privileges granted by the `user' table. If the result allows the requested operation, access is granted. Otherwise, the server checks the user's table and column privileges in the `tables_priv' and `columns_priv' tables and adds those to the user's privileges. Access is allowed or denied based on the result. It may not be apparent why the server adds the database-, table- and column-specific privileges to the global `user' entry privileges for those cases in which the `user' privileges are initially found to be insufficient for the requested operation. The reason is that a request might require more than one type of privilege. For example, if you execute an `INSERT ... SELECT' statement, you need both *insert* and *select* privileges. Your privileges might be such that the `user' table entry grants one privilege and the `db' table entry grants the other. In this case, you have the necessary privileges to perform the request, but the server cannot tell that from either table by itself; the privileges granted by both entries must be combined. The `host' table can be used to maintain a list of "secure" servers. At TcX, the `host' table contains a list of all machines on the local network. These are granted all privileges. You can also use the `host' table to indicate hosts that are *not* secure. Suppose you have a machine `public.your.domain' that is located in a public area that you do not consider secure. You can allow access to all hosts on your network except that machine with `host' table entries like this: +--------------------+----+- | Host | Db | ... +--------------------+----+- | public.your.domain | % | ... (all privileges set to 'N') | %.your.domain | % | ... (all privileges set to 'Y') +--------------------+----+- Naturally, you should always test your entries in the grant tables (e.g., using `mysqlaccess') to make sure your access privileges are actually set up the way you think they are. When privilege changes take effect ================================== When `mysqld' starts, all grant table contents are read into memory and become effective at that point. Modifications to the grant tables that you perform using `GRANT', `REVOKE', or `SET PASSWORD' are noticed by the server immediately. If you modify the grant tables manually (using `INSERT', `UPDATE', etc.), you should execute a `FLUSH PRIVILEGES' statement or run `mysqladmin flush-privileges' to tell the server to reload the grant tables. Otherwise your changes will have *no effect* until you restart the server. When the server notices that the grant tables have been changed, existing client connections are affected as follows: * Table and column privilege changes take effect with the client's next request. * Database privilege changes take effect at the next `USE db_name' command. * Global privilege and password changes take effect the next time the client connects. Setting up the initial *MySQL* privileges ========================================= After installing *MySQL*, you set up the initial access privileges by running `scripts/mysql_install_db'. *Note Quick install::. The `scripts/mysql_install_db' script starts up the `mysqld' server, then initializes the grant tables to contain the following set of privileges: * The *MySQL* `root' user is a superuser and can do anything. Connections must be made from the local host. *Note:* The initial `root' password is empty, so anyone can connect as `root' *without a password* and be granted all privileges. * Anonymous-user privileges allow anything to be done with databases that have a name of `'test'' or starting with `'test_''. Any user can connect from the local host and be treated as the anonymous user. * Other privileges are denied. For example, normal users can't use `mysqladmin shutdown' or `mysqladmin processlist'. Since your installation is initially wide open, one of the first things you should do is specify a password for the *MySQL* `root' user. You can do this as follows (note that you specify the password using the `PASSWORD()' function): shell> mysql -u root mysql mysql> UPDATE user SET Password=PASSWORD('new_password') WHERE user='root'; mysql> FLUSH PRIVILEGES; or shell> mysqladmin -u root password new_password Note that if you use the first method, which updates the password in the `user' table directly, you have to tell the server to reread the grant tables (with `FLUSH PRIVILEGES'), since the change will go unnoticed otherwise. Once the `root' password has been set, you must supply that password whenever you connect to the server as `root'. You may wish to leave the `root' password blank so that you don't need to specify it while you perform additional setup or testing, but be sure to set it before using your installation for any real production work. See the `scripts/mysql_install_db' script to see how it sets up the default privileges. You can use this as a basis to see how to add other users. If you want the initial privileges to be different than those just described above, you can modify `mysql_install_db' before you run it. To recreate the grant tables completely, remove all the `*.ISM' and `*.ISD' files in the directory containing the `mysql' database. (This is the directory named `mysql' under the database directory, which is listed when you run `mysqld --help'.) Then run the `mysql_install_db' script, possibly after editing it first to have the privileges you want. Adding new user privileges to *MySQL* ===================================== You can add users in two different ways: by using `GRANT' statements or by manipulating the *MySQL* grant tables directly. Use of `GRANT' statements is the preferred method. The examples below show how to use the `mysql' client to set up new users. These examples assume that privileges are set up according to the defaults described in the previous section. This means that to make changes, you must be on the same machine where `mysqld' is running, and you must connect as the *MySQL* `root' user, and the `root' user must have the *insert* privilege for the `mysql' database and the *reload* administrative privilege. If you have changed the `root' user password, you must also specify it for the `mysql' commands below. You can add new users by issuing `GRANT' statements: shell> mysql --user=root mysql mysql> GRANT ALL PRIVILEGES ON *.* TO monty@localhost IDENTIFIED BY 'something' WITH GRANT OPTION; mysql> GRANT ALL PRIVILEGES ON *.* TO monty@"%" IDENTIFIED BY 'something' WITH GRANT OPTION; mysql> GRANT RELOAD,PROCESS ON *.* TO admin@localhost; mysql> GRANT USAGE ON *.* TO dummy@localhost; These `GRANT' statements set up three new users: `monty' A full superuser who can connect to the server from anywhere, but who must use a password to do so. Note that we must issue `GRANT' statements for both `monty@localhost' and `monty@"%"'. If we don't add the entry with `localhost', the anonymous user entry for `localhost' that is created by `mysql_install_db' will take precedence when we connect from the local host, because it has a more specific `Host' field value and comes earlier in the sort order. `admin' A user who can connect from `localhost' without a password and who is granted the *reload* and *process* administrative privileges. This allows the user to execute the `mysqladmin reload', `mysqladmin refresh' and `mysqladmin flush-*' commands, as well as `mysqladmin processlist' . No database-related privileges are granted. They could be granted later by issuing additional `GRANT' statements. `dummy' A user who can connect without a password, but only from the local host. The global privileges are all set to `'N'' because the privilege type is `USAGE', which allows you to set up a user with no privileges. It is assumed that you would grant database-specific privileges later. You can also add the same user access information directly by issuing `INSERT' statements and then telling the server to reload the grant tables: shell> mysql --user=root mysql mysql> INSERT INTO user VALUES('localhost','monty',PASSWORD('something'), 'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y') mysql> INSERT INTO user VALUES('%','monty',PASSWORD('something'), 'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y') mysql> INSERT INTO user SET Host='localhost',User='admin', Reload_priv='Y', Process_priv='Y'; mysql> INSERT INTO user (Host,User,Password) VALUES('localhost','dummy',''); mysql> FLUSH PRIVILEGES; Note that depending on your *MySQL* version, you may have to use a different number of `'Y'' values above. The extended (more readable) `INSERT' syntax that is available starting with 3.22.11 is used here for the `admin' user. Note that to set up a superuser, you need only create a `user' table entry with the privilege fields set to `'Y''. No `db' or `host' table entries are necessary. The privilege columns in the `user' table were not set explicitly in the last `INSERT' statement (for the `dummy' user), so those columns are assigned the default value of `'N''. The following example adds a user `custom' who can connect from hosts `localhost', `server.domain' and `whitehouse.gov'. He wants to access the `bankaccount' database only from `localhost', the `expenses' database only from `whitehouse.gov' and the `customer' database from all three hosts. He wants to use the password `stupid' from all three hosts. To set up this user's privileges using `GRANT' statements, run these commands: shell> mysql --user=root mysql mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP ON bankaccount.* TO custom@localhost IDENTIFIED BY 'stupid'; mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP ON expenses.* TO custom@whitehouse.gov IDENTIFIED BY 'stupid'; mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP ON customer.* TO custom@'%' IDENTIFIED BY 'stupid'; To set up the user's privileges by modifying the grant tables directly, run these commands (note the `FLUSH PRIVILEGES' at the end): shell> mysql --user=root mysql mysql> INSERT INTO user (Host,User,Password) VALUES('localhost','custom',PASSWORD('stupid')); mysql> INSERT INTO user (Host,User,Password) VALUES('server.domain','custom',PASSWORD('stupid')); mysql> INSERT INTO user (Host,User,Password) VALUES('whitehouse.gov','custom',PASSWORD('stupid')); mysql> INSERT INTO db (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv, Create_priv,Drop_priv) VALUES ('localhost','bankaccount','custom','Y','Y','Y','Y','Y','Y'); mysql> INSERT INTO db (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv, Create_priv,Drop_priv) VALUES ('whitehouse.gov','expenses','custom','Y','Y','Y','Y','Y','Y'); mysql> INSERT INTO db (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv, Create_priv,Drop_priv) VALUES('%','customer','custom','Y','Y','Y','Y','Y','Y'); mysql> FLUSH PRIVILEGES; The first three `INSERT' statements add `user' table entries that allow user `custom' to connect from the various hosts with the given password, but grant no permissions to him (all privileges are set to the default value of `'N''). The next three `INSERT' statements add `db' table entries that grant privileges to `custom' for the `bankaccount', `expenses' and `customer' databases, when accessed from the proper hosts. As usual, when the grant tables are modified directly, the server must be told to reload the grant tables so that the changes take effect. If you want to give a specific user access from any machine in a given domain, you can issue a `GRANT' statement like the following: mysql> GRANT ... ON *.* TO myusername@"%.mydomainname.com" IDENTIFIED BY 'mypassword'; To do the same thing by modifying the grant tables directly, do this: mysql> INSERT INTO user VALUES ('%.mydomainname.com', 'myusername', PASSWORD('mypassword'),...); mysql> FLUSH PRIVILEGES; You can also use `xmysqladmin', `mysql_webadmin' and even `xmysql' to insert, change and update values in the grant tables. You can find these utilities at `http://www.tcx.se/Contrib'. How to set up passwords ======================= The examples in the preceding sections illustrate an important principle: when you store a non-empty password using `INSERT' or `UPDATE' statements, you must use the `PASSWORD()' function to encrypt it. This is because the `user' table stores passwords in encrypted form, not as plaintext. If you forget that fact, you are likely to attempt to set passwords like this: shell> mysql -u root mysql mysql> INSERT INTO user (Host,User,Password) VALUES('%','jeffrey','bLa81m0'); mysql> FLUSH PRIVILEGES; The result is that the plaintext value `'bLa81m0'' is stored as the password in the `user' table. When the user `jeffrey' attempts to connect to the server using this password, the `mysql' client encrypts it and sends the result to the server. The server compares the value in the `user' table (which is the plaintext value `'bLa81m0'') to the encrypted password (which is *not* `'bLa81m0''). The comparison fails and the server rejects the connection: shell> mysql -u jeffrey -pbLa81m0 test Access denied Since passwords must be encrypted when they are inserted in the `user' table, the `INSERT' statement should have been specified like this instead: mysql> INSERT INTO user (Host,User,Password) VALUES('%','jeffrey',PASSWORD('bLa81m0')); You must also use the `PASSWORD()' function when you use `SET PASSWORD' statements: mysql> SET PASSWORD FOR jeffrey@"%" = PASSWORD('bLa81m0'); Note: The `PASSWORD()' function performs password encryption, but it does not do so in the same way that Unix passwords are encrypted. You should not assume that if your Unix password and your *MySQL* password are the same, `PASSWORD()' will result in the same encrypted value as is stored in the Unix password file. If you set passwords using the `GRANT ... IDENTIFIED BY' statement or the `mysqladmin password' command, the `PASSWORD()' function is unnecessary. They both take care of encrypting the password for you: mysql> GRANT USAGE ON *.* TO jeffrey@"%" IDENTIFIED BY 'bLa81m0'; shell> mysqladmin -u jeffrey password bLa81m0 Causes of `Access denied' errors ================================ If you encounter `Access denied' errors when you try to connect to the *MySQL* server, the list below indicates some courses of action you can take to correct the problem: * Did you run the `mysql_install_db' script after installing *MySQL*, to set up the initial grant table contents? If not, do so. *Note Default privileges::. Test these initial privileges by executing this command: shell> mysql -u root test The server should let you connect without error. You should also make sure you have a file `user.ISD' in the *MySQL* database directory (ordinarily, this is `PATH/var/mysql/user.ISD', where `PATH' is the pathname to the *MySQL* installation root). * After a fresh installation, you should connect to the server and set up your users and access permissions: shell> mysql -u root mysql The server should let you connect because the *MySQL* `root' user has no password initially. Since that is also a security risk, setting the `root' password is something you should do while you're setting up your other *MySQL* users. If you try to connect as `root' and get this error: Access denied for user: '@unknown' to database mysql this means that you don't have an entry in the `user' table with the `User' column = `root' and that `mysqld' cannot resolve the hostname for your client. In this case, you must restart the server with the `--skip-grant-tables' option and edit your `/etc/hosts' or `\windows\hosts' file to add a entry for your host. * If you updated an existing *MySQL* installation from a pre-3.22.11 version to version 3.22.11 or later, did you run the `mysql_fix_privilege_tables' script? If not, do so. The structure of the grant tables changed with *MySQL* 3.22.11 when the `GRANT' statement became functional. * If you make changes to the grant tables directly (using `INSERT' or `UPDATE' statement) and your changes seem to be ignored, remember that you must issue a `FLUSH PRIVILEGES' statement or execute a `mysqladmin flush-privileges' command to cause the server to reread the tables. Otherwise your changes have no effect until the next time the server is restarted. Remember that after you set the `root' password, you won't need to specify it until after you flush the privileges, because the server still won't know you've changed the password yet! * If your privileges seem to have changed in the middle of a session, it may be that a superuser has changed them. Reloading the grant tables affects new client connections, but it also affects existing connections as indicated in *Note Privilege changes::. * For testing, start the `mysqld' daemon with the `--skip-grant-tables' option. Then you can change the *MySQL* grant tables and use the `mysqlaccess' script to check whether or not your modifications have the desired effect. When you are satisfied with your changes, execute `mysqladmin flush-privileges' to tell the `mysqld' server to start using the new grant tables. *Note:* reloading the grant tables overrides the `--skip-grant-tables' option. This allows you to tell the server to begin using the grant tables again without bringing it down and restarting it. * If you have access problems with a Perl, Python or ODBC program, try to connect to the server with `mysql -u user_name db_name' or `mysql -u user_name -pyour_pass db_name'. (Notice that there is no space between `-p' and the password; you can also use the `--password=your_pass' syntax to specify the password.) If you are able to connect using the `mysql' client, there is a problem with your program and not with the access privileges. * If you can't get your password to work, remember that you must use the `PASSWORD()' function if you set the password with the `INSERT', `UPDATE' or `SET PASSWORD' statements. The `PASSWORD()' function is unnecessary if you specify the password using the `GRANT ... INDENTIFIED BY' statement or the `mysqladmin password' command. *Note Passwords::. * `localhost' is a synonym for your local hostname, and is also the default host to which clients try to connect if you specify no host explicitly. However, connections to `localhost' do not work if you are running on a system that uses MIT-pthreads (`localhost' connections are made using Unix sockets, which are not supported by MIT-pthreads). To avoid this problem on such systems, you should use the `--host' option to name the server host explicitly. This will make a TCP/IP connection to the `mysqld' server. In this case, you must have your real hostname in `user' table entries on the server host. (This is true even if you are running a client program on the same host as the server.) * If you get an `Access denied' error when trying to connect to the database with `mysql -u user_name db_name', you may have a problem with the `user' table. Check this by executing `mysql -u root mysql' and issuing this SQL statement: mysql> SELECT * FROM user; The result should include an entry with the `Host' and `User' columns matching your computer's hostname and your *MySQL* user name. * The `Access denied' error message will tell you who you are trying to log in as, the host from which you are trying to connect, and whether or not you were using a password. Normally, you should have one entry in the `user' table that exactly matches the hostname and user name that were given in the error message. * If you get the following error when you try to connect from another machine to the *MySQL* server, then there is no row in the `user' table that matches the host from which you are trying to connect: Host ... is not allowed to connect to this MySQL server You can fix this by using the command line tool `mysql' (on the server host!) to add a row to the `user' table for the user/hostname combination from which you are trying to connect. If you are not running *MySQL* 3.22 and you don't know the IP number or hostname of the machine from which you are connecting, you should put an entry with `'%'' as the `Host' column value in the `user' table and restart `mysqld' with the `--log' option on the server machine. After trying to connect from the client machine, the information in the *MySQL* log will indicate how you really did connect. (Then replace the `'%'' in the `user' table entry with the actual hostname that shows up in the log. Otherwise, you'll have a system that is insecure.) * If `mysql -u root test' works but `mysql -h your_hostname -u root test' results in `Access denied', then you may not have the correct name for your host in the `user' table. A common problem here is that the `Host' value in the user table entry specifies an unqualified hostname, but your system's name resolution routines return a fully-qualified domain name (or vice-versa). For example, if you have an entry with host `'tcx'' in the `user' table, but your DNS tells *MySQL* that your hostname is `'tcx.subnet.se'', the entry will not work. Try adding an entry to the `user' table that contains the IP number of your host as the `Host' column value. (Alternatively, you could add an entry to the `user' table with a `Host' value that contains a wildcard--for example, `'tcx.%''. However, use of hostnames ending with `%' is *insecure* and is *not* recommended!) * If `mysql -u user_name test' works but `mysql -u user_name other_db_name' doesn't work, you don't have an entry for `other_db_name' listed in the `db' table. * If `mysql -u user_name db_name' works when executed on the server machine, but `mysql -u host_name -u user_name db_name' doesn't work when executed on another client machine, you don't have the client machine listed in the `user' table or the `db' table. * If you can't figure out why you get `Access denied', remove from the `user' table all entries that have `Host' values containing wildcards (entries that contain `%' or `_'). A very common error is to insert a new entry with `Host'=`'%'' and `User'=`'some user'', thinking that this will allow you to specify `localhost' to connect from the same machine. The reason that this doesn't work is that the default privileges include an entry with `Host'=`'localhost'' and `User'=`'''. Since that entry has a `Host' value `'localhost'' that is more specific than `'%'', it is used in preference to the new entry when connecting from `localhost'! The correct procedure is to insert a second entry with `Host'=`'localhost'' and `User'=`'some_user'', or to remove the entry with with `Host'=`'localhost'' and `User'=`'''. * If you get the error: Access to database denied you may have a problem with the `db' or `host' table. If the entry selected from the `db' table has an empty value in the `Host' column, make sure there are one or more corresponding entries in the `host' table specifying to which hosts the `db' table entry applies. * If you get the error: Access to database denied when using the SQL commands `SELECT ... INTO OUTFILE' or `LOAD DATA INFILE', your entry in the `user' table probably doesn't have the *file* privilege enabled. * If everything else fails, start the `mysqld' daemon with a debugging option (for example, `--debug=d,general,query'). This will print host and user information about attempted connections, as well as information about each command issued. *Note Debugging::. * If you have any other problems with the *MySQL* grant tables and feel you must post the problem to the mailing list, always provide a dump of the *MySQL* grant tables. You can dump the tables with the `mysqldump mysql' command. As always, post your problem using the `mysqlbug' script. * If you get either of these errors, then either the `mysqld' daemon is not running or you are trying to connect to the wrong socket or port: Can't connect to local MySQL server Can't connect to MySQL server on some_hostname First see if the mysqld deamon is really running (with `ps'). Check after this that the socket file exists (normally `/tmp/mysql.sock') or try to connect to the port with `telnet host_name 3306'. You can also try `mysqladmin version' and `mysqladmin -h host_name version' to get some more information. Also, check the error logs in the *MySQL* data directory to see if they can provide some hints. * Remember that client programs will use connection parameters specified in configuration files or environment variables. If a client seems to be sending the wrong default connection parameters when you don't specify them on the command line, check your environment and the `.my.cnf' file in your home directory. You might also check the system-wide *MySQL* configuration files, though it is far less likely that connection parameters will be specified there. If you get `Access denied' when you run a client without any options, make sure you haven't specified an old password in any of your option files! *Note Option files::. How to make *MySQL* secure against crackers =========================================== To make a *MySQL* system secure, you should strongly consider the following suggestions: * Use passwords for all *MySQL* users. Remember that anyone can log in as any other person as simply as `mysql -u other_user db_name' if `other_user' has no password. This is common behavior with client/server applications. You can change the password of all users by editing the `mysql_install_db' script before you run it, or only the password for the *MySQL* `root' user like this: shell> mysql -u root mysql mysql> UPDATE user SET Password=PASSWORD('new_password') WHERE user='root'; mysql> FLUSH PRIVILEGES; * Don't start the *MySQL* daemon as the Unix `root' user. `mysqld' can be run as any user. You can also create a new Unix user `mysql' to make everything even more secure. If you run `mysqld' as another Unix user, you don't need to change the `root' user name in the `user' table, because *MySQL* user names have nothing to do with Unix user names. You can edit the `mysql.server' script to start `mysqld' as another Unix user. Normally this is done with the `su' command. For more details, see *Note Changing *MySQL* user: Changing MySQL user. * Check that the user that `mysqld' runs as is the only Unix user with read/write privileges in the database directories. * Don't give the *process* privilege to all users. The output of `mysqladmin processlist' shows the text of the currently executing queries, so any user who is allowed to execute that command might be able to see if another user issues an `UPDATE user SET password=PASSWORD('not_secure')' query. `mysqld' saves an extra connection for users who have the *process* privilege, so that a *MySQL* `root' user can log in and check things even if all normal connections are in use. * Don't give the *file* privilege to all users. Any user that has this privilege can write a file anywhere in the file system with the privileges of the `mysqld' daemon! To make this a bit safer, all files generated with `SELECT ... INTO OUTFILE' are readable to everyone, and you can't overwrite existing files. * If you don't trust your DNS, you should use IP numbers instead of hostnames in the grant tables. In principle, the `--secure' option to `mysqld' should make hostnames safe. In any case, you should be very careful about using hostname values that contain wildcards! * If you put a password for the Unix `root' user in the `mysql.server' script, make sure this script is readable only by `root'. The following `mysqld' options affect security: `--secure' IP numbers returned by the `gethostbyname()' system call are checked to make sure they resolve back to the original hostname. This makes it harder for someone on the outside to get access by simulating another host. This option also adds some sanity checks of hostnames. The option is turned off by default in *MySQL* 3.21 since it sometimes takes a long time to perform backward resolutions. *MySQL* 3.22 caches hostnames and has this option enabled by default. `--skip-grant-tables' This option causes the server not to use the privilege system at all. This gives everyone *full access* to all databases! (You can tell a running server to start using the grant tables again by executing `mysqladmin reload'.) `--skip-name-resolve' Hostnames are not resolved. All `Host' column values in the grant tables must be IP numbers or `localhost'. `--skip-networking' Don't allow TCP/IP connections over the network. All connections to `mysqld' must be made via Unix sockets. This option doesn't work very well on systems that use MIT-pthreads, because the MIT-pthreads package doesn't support Unix sockets. *MySQL* language reference ************************** Literals: how to write strings and numbers ========================================== Strings ------- A string is a sequence of characters, surrounded by either single quote (`'') or double quote (`"') characters. Examples: 'a string' "another string" Within a string, certain sequences have special meaning. Each of these sequences begins with a backslash (`\'), known as the *escape character*. *MySQL* recognizes the following escape sequences: `\0' An ASCII 0 (`NUL') character. `\n' A newline character. `\t' A tab character. `\r' A carriage return character. `\b' A backspace character. `\'' A single quote (`'') character. `\"' A double quote (`"') character. `\\' A backslash (`\') character. `\%' A `%' character. This is used to search for literal instances of `%' in contexts where `%' would otherwise be interpreted as a wildcard character. `\_' A `_' character. This is used to search for literal instances of `_' in contexts where `_' would otherwise be interpreted as a wildcard character. There are several ways to include quotes within a string: * A `'' inside a string quoted with `'' may be written as `'''. * A `"' inside a string quoted with `"' may be written as `""'. * You can precede the quote character with an escape character (`\'). * A `'' inside a string quoted with `"' needs no special treatment and need not be doubled or escaped. In the same way, `"' inside a string quoted with `'' needs no special treatment. The `SELECT' statements shown below demonstrate how quoting and escaping work: mysql> SELECT 'hello', '"hello"', '""hello""', 'hel''lo', '\'hello'; +-------+---------+-----------+--------+--------+ | hello | "hello" | ""hello"" | hel'lo | 'hello | +-------+---------+-----------+--------+--------+ | hello | "hello" | ""hello"" | hel'lo | 'hello | +-------+---------+-----------+--------+--------+ mysql> SELECT "hello", "'hello'", "''hello''", "hel""lo", "\"hello"; +-------+---------+-----------+--------+--------+ | hello | 'hello' | ''hello'' | hel"lo | "hello | +-------+---------+-----------+--------+--------+ | hello | 'hello' | ''hello'' | hel"lo | "hello | +-------+---------+-----------+--------+--------+ mysql> SELECT "This\nIs\nFour\nlines"; +--------------------+ | This Is Four lines | +--------------------+ | This Is Four lines | +--------------------+ If you want to insert binary data into a `BLOB' column, the following characters must be represented by escape sequences: `NUL' ASCII 0. Should be represented by `\0' (a backslash and an ASCII `0' character). `\' ASCII 92, backslash `'' ASCII 39, single quote `"' ASCII 34, double quote If you write C code, you can use the C API function `mysql_escape_string()' to escape characters for the `INSERT' clause. *Note C API function overview::. In Perl, you can use the `quote' method of the `DBI' package to convert special characters to the proper escape sequences. *Note Perl `DBI' Class: Perl DBI Class. You should use an escape function on every possible string that may contain any of the special characters listed above! Numbers ------- Integers are just a sequence of digits. Floats use `.' as a decimal separator. Examples of valid numbers: 1221 294.42 -32032.6809e+10 `NULL' values ------------- When using the text file export formats (`SELECT ... INTO OUTFILE'), `NULL' may be represented by `\N'. *Note Load::. Note that `NULL' means "no data" and is different from values such as `0' for numeric types and the empty string for string types. *Note Problems with NULL::. Database, table, index, column and alias names ---------------------------------------------- Database, table, index, column and alias names all follow the same rules in *MySQL*: * A name consists of alphanumeric characters from the current character set and also `_' and `$'. The default character set is ISO-8859-1 Latin1; this may be changed by recompiling *MySQL*. * A database, table, index or column name can have up to 64 characters. An alias name can have up to 256 characters. * A name may start with any character that is legal in a name. In particular, a name may start with a number (which is different than many other systems!). However, a name cannot consist *only* of numbers. * It is recommended that you do not use names like `1e', because an expression like `1e+1' is ambiguous. It may be interpreted as the expression `1e + 1' or as the number `1e+1'. * You cannot use the `.' character in names because it is used to extend the format by which you can refer to columns (see below). In *MySQL* you can refer to a column using any of the following forms: *Column reference* *Meaning* `col_name' Column `col_name' from whichever table that is used in the query contains a column named `col_name' `tbl_name.col_name' Column `col_name' from table `tbl_name' of the current database `db_name.tbl_name.col_name'Column `col_name' from table `tbl_name' of the database `db_name'. This form is not available in versions of *MySQL* prior to 3.22. You need not specify a `tbl_name' or `db_name.tbl_name' prefix for a column reference in a statement unless the reference would be ambiguous. For example, suppose tables `t1' and `t2' each contain a column `c', and you retrieve `c' in a `SELECT' statement that uses both `t1' and `t2'. In this case, `c' is ambiguous because it is not unique among the tables used in the statement, so you must indicate which table you mean by writing `t1.c' or `t2.c'. Similarly, if you are retrieving from a table `t' in database `db1' and from a table `t' in database `db2', you must refer to columns in those tables as `db1.t.col_name' and `db2.t.col_name'. The syntax `.tbl_name' means the table `tbl_name' in the current database. This syntax is accepted because some ODBC prefix table names with a `.' character. Case sensitivity in names ......................... Database and table names are case sensitive in Unix and case insensitive in Win32, because directory and file names are case sensitive in Unix but not in Win32. (In *MySQL*, databases and tables correspond to directories and files within those directories, so the case sensitivity of the underlying operating system determines how *MySQL* behaves.) *Note:* although database and file names are case insensitive for Win32, you should not refer to a given database or table using different cases within the same query. Column names are case insensitive in all cases. Aliases on tables are case sensitive and aliases on columns are case insensitive. Column types ============ *MySQL* supports a number of column types, which may be grouped into three categories: numeric types, date and time types, and string (or character) types. This section first gives an overview of the types available, then summarizes the storage requirements for each column type and provides a more detailed description of the properties of the types in each category. The overview is intentionally brief. The more detailed descriptions should be consulted for additional information about particular column types, such as the allowable formats in which you can specify values. The column types supported by *MySQL* are listed below. The following code letters are used in the descriptions: * `M' indicates the maximum display size. * `D' applies to floating-point types and indicates the number of digits following the decimal point. Square brackets (`[' and `]') indicate parts of type specifiers that are optional. `TINYINT[(M)] [UNSIGNED] [ZEROFILL]' A very small integer. The signed range is `-128' to `127'. The unsigned range is `0' to `255'. `SMALLINT[(M)] [UNSIGNED] [ZEROFILL]' A small integer. The signed range is `-32768' to `32767'. The unsigned range is `0' to `65535'. `MEDIUMINT[(M)] [UNSIGNED] [ZEROFILL]' A medium-size integer. The signed range is `-8388608' to `8388607'. The unsigned range is `0' to `16777215'. `INT[(M)] [UNSIGNED] [ZEROFILL]' A normal-size integer. The signed range is `-2147483648' to `2147483647'. The unsigned range is `0' to `4294967295'. `INTEGER[(M)] [UNSIGNED] [ZEROFILL]' This is a synonym for `INT'. `BIGINT[(M)] [UNSIGNED] [ZEROFILL]' A large integer. The signed range is `-9223372036854775808' to `9223372036854775807'. The unsigned range is `0' to `18446744073709551615'. Note that all arithmetic is done using signed `BIGINT' or `DOUBLE' values, so you shouldn't use unsigned big integers larger than `9223372036854775807' (63 bits) except with bit functions! Note that `-', `+' and `*' will use `BIGINT' arithmetic when both arguments are `INTEGER' values! This means that if you multiply two big integers (or results from functions that return integers) you may get unexpected results if the result is bigger than `9223372036854775807'. `FLOAT(precision) [ZEROFILL]' A floating-point number. Cannot be unsigned. `precision' can be `4' or `8'. `FLOAT(4)' is a single-precision number and `FLOAT(8)' is a double-precision number. These types are like the `FLOAT' and `DOUBLE' types described immediately below. `FLOAT(4)' and `FLOAT(8)' have the same ranges as the corresponding `FLOAT' and `DOUBLE' types, but their display size and number of decimals is undefined. This syntax is provided for ODBC compatibility. `FLOAT[(M,D)] [ZEROFILL]' A small (single-precision) floating-point number. Cannot be unsigned. Allowable values are `-3.402823466E+38' to `-1.175494351E-38', `0' and `-1.175494351E-38' to `3.402823466E+38'. `DOUBLE[(M,D)] [ZEROFILL]' A normal-size (double-precision) floating-point number. Cannot be unsigned. Allowable values are `-1.7976931348623157E+308' to `-2.2250738585072014E-308', `0' and `2.2250738585072014E-308' to `1.7976931348623157E+308'. `DOUBLE PRECISION[(M,D)] [ZEROFILL]' `REAL[(M,D)] [ZEROFILL]' These are synonyms for `DOUBLE'. `DECIMAL(M,D) [ZEROFILL]' An unpacked floating-point number. Cannot be unsigned. Behaves like a `CHAR' column (`unpacked' means the number is stored as a string, using one character for each digit of the value, the decimal point, and, for negative numbers, the `-' sign). If `D' is 0, values will have no decimal point or fractional part. The maximum range of `DECIMAL' values is the same as for `DOUBLE', but the actual range for a given `DECIMAL' column may be constrained by the choice of `M' and `D'. `NUMERIC(M,D) [ZEROFILL]' This is a synonym for `DECIMAL'. `DATE' A date. The supported range is `'1000-01-01'' to `'9999-12-31''. *MySQL* displays `DATE' values in `'YYYY-MM-DD'' format, but allows you to assign values to `DATE' columns using either strings or numbers. `DATETIME' A date and time combination. The supported range is `'1000-01-01 00:00:00'' to `'9999-12-31 23:59:59''. *MySQL* displays `DATETIME' values in `'YYYY-MM-DD HH:MM:SS'' format, but allows you to assign values to `DATETIME' columns using either strings or numbers. `TIMESTAMP[(M)]' A timestamp. The range is `'1970-01-01 00:00:00'' to sometime in the year `2106'. *MySQL* displays `TIMESTAMP' values in `YYYYMMDDHHMMSS', `YYMMDDHHMMSS', `YYYYMMDD' or `YYMMDD' format, depending on whether `M' is `14' (or missing), `12', `8' or `6', but allows you to assign values to `TIMESTAMP' columns using either strings or numbers. A `TIMESTAMP' column is useful for recording the time of an `INSERT' or `UPDATE' operation because it is automatically set to the time of the last operation. You can also set it to the current time by giving it a `NULL' value. *Note Date and time types::. `TIME' A time. The range is `'-838:59:59'' to `'838:59:59''. *MySQL* displays `TIME' values in `'HH:MM:SS'' format, but allows you to assign values to `TIME' columns using either strings or numbers. `YEAR' A year. The allowable values are `1901' to `2155', and `0000'. *MySQL* displays `YEAR' values in `YYYY' format, but allows you to assign values to `YEAR' columns using either strings or numbers. (`YEAR' is a new type for *MySQL* 3.22.) `CHAR(M) [BINARY]' A fixed-length string that is always right-padded with spaces to the specified length when stored. The range of `M' is 1 to 255 characters. Trailing spaces are removed when the value is retrieved. `CHAR' values are sorted and compared in case-insensitive fashion unless the `BINARY' keyword is given. `VARCHAR(M) [BINARY]' A variable-length string. NOTE: Trailing spaces are removed when the value is stored (this differs from the ANSI SQL specification). The range of `M' is 1 to 255 characters. `VARCHAR' values are sorted and compared in case-insensitive fashion unless the `BINARY' keyword is given. `TINYBLOB' `TINYTEXT' A `BLOB' or `TEXT' column with a maximum length of 255 (2^8 - 1) characters. `BLOB' `TEXT' A `BLOB' or `TEXT' column with a maximum length of 65535 (2^16 - 1) characters. `MEDIUMBLOB' `MEDIUMTEXT' A `BLOB' or `TEXT' column with a maximum length of 16777215 (2^24 - 1) characters. `LONGBLOB' `LONGTEXT' A `BLOB' or `TEXT' column with a maximum length of 4294967295 (2^32 - 1) characters. `ENUM('value1','value2',...)' An enumeration. A string object that can have only one value, chosen from the list of values `'value1', 'value2',...' (or `NULL'). An `ENUM' can have a maxiumum of 65535 distinct values. `SET('value1','value2',...)' A set. A string object that can have zero or more values, each of which must be chosen from the list of values `'value1', 'value2',...' A `SET' can have a maximum of 64 members. Column type storage requirements -------------------------------- The storage requirements for each of the column types supported by *MySQL* are listed below by category. Numeric types ------------- *Column type* *Storage required* `TINYINT' 1 byte `SMALLINT' 2 bytes `MEDIUMINT' 3 bytes `INT' 4 bytes `INTEGER' 4 bytes `BIGINT' 8 bytes `FLOAT(4)' 4 bytes `FLOAT(8)' 8 bytes `FLOAT' 4 bytes `DOUBLE' 8 bytes `DOUBLE PRECISION' 8 bytes `REAL' 8 bytes `DECIMAL(M,D)' `M' bytes (`D'+2, if `M < D') `NUMERIC(M,D)' `M' bytes (`D'+2, if `M < D') Date and time types ------------------- *Column type* *Storage required* `DATETIME' 8 bytes `DATE' 3 bytes `TIMESTAMP' 4 bytes `TIME' 3 bytes `YEAR' 1 byte String types ------------ *Column type* *Storage required* `CHAR(M)' `M' bytes, `1 <= M <= 255' `VARCHAR(M)' `L'+1 bytes, where `L <= M' and `1 <= M <= 255' `TINYBLOB', `TINYTEXT' `L'+1 bytes, where `L' < 2^8 `BLOB', `TEXT' `L'+2 bytes, where `L' < 2^16 `MEDIUMBLOB', `L'+3 bytes, where `L' < 2^24 `MEDIUMTEXT' `LONGBLOB', `LONGTEXT' `L'+4 bytes, where `L' < 2^32 `ENUM('value1','value2',...)'1 or 2 bytes, depending on the number of enumeration values (65535 values maximum) `SET('value1','value2',...)'1, 2, 3, 4 or 8 bytes, depending on the number of set members (64 members maximum) `VARCHAR' and the `BLOB' and `TEXT' types are variable-length types, for which the storage requirements depend on the actual length of column values (represented by `L' in the preceding table), rather than on the type's maximum possible size. For example, a `VARCHAR(10)' column can hold a string with a maximum length of 10 characters. The actual storage required is the length of the string (`L'), plus 1 byte to record the length of the string. For the string `'abcd'', `L' is 4 and the storage requirement is 5 bytes. The `BLOB' and `TEXT' types require 1, 2, 3 or 4 bytes to record the length of the column value, depending on the maxiumum possible length of the type. If a table includes any variable-length column types, the record format will also be variable-length. Note that when a table is created, *MySQL* may under certain conditions change a column from a variable-length type to a fixed-length type, and vice-versa. *Note Create table::. The size of an `ENUM' object is determined by the number of different enumeration values. 1 byte is used for enumerations with up to 255 possible values. 2 bytes are used for enumerations with up to 65535 values. The size of a `SET' object is determined by the number of different set members. If the set size is `N', the object occupies `(N+7)/8' bytes, rounded up to 1, 2, 3, 4 or 8 bytes. A `SET' can have a maximum of 64 members. Numeric types ------------- All integer types can have an optional attribute `UNSIGNED'. Unsigned values can be used when you want to allow only positive numbers in a column and you need a little bigger numeric range for the column. All numeric types can have an optional attribute `ZEROFILL'. Values for `ZEROFILL' columns are left-padded with zeroes up to the maximum display length when they are displayed. For example, for a column declared as `INT(5) ZEROFILL', a value of 4 is retrieved as `00004'. When asked to store a value in a numeric column that is outside the column type's allowable range, *MySQL* clips the value to the appropriate endpoint of the range and stores the resulting value instead. For example, the range of an `INT' column is `-2147483648' to `2147483647'. If you try to insert `-9999999999' into an `INT' column, the value is clipped to the lower endpoint of the range, and `-2147483648' is stored instead. Similarly, if you try to insert `9999999999', `2147483647' is stored instead. If the `INT' column is `UNSIGNED', the size of the column's range is the same but its endpoints shift up to `0' and `4294967295'. If you try to store `-9999999999' and `9999999999', the values stored in the column become `0' and `4294967296'. Conversions that occur due to clipping are reported as `warnings' for `ALTER TABLE', `LOAD DATA INFILE', `UPDATE' and multi-row `INSERT' statements. The maximum display size (`M') and number of decimals (`D') are used for formatting and calculation of maximum column width. *MySQL* will store any value that fits a column's storage type even if the value exceeds the display size. For example, an `INT(4)' column has a display size of 4. Suppose you insert a value which has more than 4 digits into the column, such as `12345'. The display size is exceeded, but the allowable range of the `INT' type is not, so *MySQL* stores the actual value, `12345'. When retrieving the value from the column, *MySQL* returns the actual value stored in the column. The `DECIMAL' type is considered a numeric type (as is its synonym, `NUMERIC'), but such values are stored as strings. One character is used for each digit of the value, the decimal point (if `D' > 0) and the `-' sign (for negative numbers). If `D' is 0, `DECIMAL' and `NUMERIC' values contain no decimal point or fractional part. The maximum range of `DECIMAL' values is the same as for `DOUBLE', but the actual range for a given `DECIMAL' column may be constrained by the choice of `M' and `D'. For example, a type specification such as `DECIMAL(4,2)' indicates a maximum length of four characters with two digits after the decimal point. Due to the way the `DECIMAL' type is stored, this specification results in an allowable range of `-.99' to `9.99', much less than the range of a `DOUBLE'. To avoid some rounding problems, *MySQL* always rounds everything that it stores in any floating-point column according to the number of decimals. Suppose you have a column type of `FLOAT(8,2)'. The number of decimals is 2, so a value such as `2.333' is rounded to two decimals and stored as `2.33'. Date and time types ------------------- The date and time types are `DATETIME', `DATE', `TIMESTAMP', `TIME' and `YEAR'. Each of these has a range of legal values, as well as a `zero' value that is used when you specify an illegal value. Here are some general considerations to keep in mind when working with date and time types: * *MySQL* retrieves values for a given date or time type in a standard format, but it attempts to interpret a variety of formats for values that you supply (e.g., when you specify a value to be assigned to or compared to a date or time type). Nevertheless, only the formats described in the following sections are supported. It is expected that you will supply legal values, and unpredictable results may occur if you use values in other formats. * Although *MySQL* tries to interpret values in several formats, it always expects the year part of date values to be leftmost. Dates must be given in year-month-day order (e.g., `'98-09-04''), rather than in the month-day-year or day-month-year orders commonly used elsewhere (e.g., `'09-04-98'', `'04-09-98''). * *MySQL* automatically converts a date or time type value to a number if the value is used in a numeric context, and vice versa. * When *MySQL* encounters a value for a date or time type that is out of range or otherwise illegal for the type, it converts the value to the `zero' value for that type. (The exception is that out-of-range `TIME' values are clipped to the appropriate endpoint of the `TIME' range.) The table below shows the format of the `zero' value for each type: *Column type* *`Zero' value* `DATETIME' `'0000-00-00 00:00:00'' `DATE' `'0000-00-00'' `TIMESTAMP' `00000000000000' (length depends on display size) `TIME' `'00:00:00'' `YEAR' `0000' * The `zero' values are special, but you can store or refer to them explicitly using the values shown in the table. You can also do this using the values `'0'' or `0', which are easier to write. * `Zero' date or time values used through *MyODBC* are converted automatically to `NULL' in *MyODBC* 2.50.12 and above, because ODBC can't handle such values. The `DATETIME', `DATE' and `TIMESTAMP' types ............................................ The `DATETIME', `DATE' and `TIMESTAMP' types are related. This section describes how they are similar and how they differ. The `DATETIME' type is used when you need values that contain both date and time information. *MySQL* retrieves and displays `DATETIME' values in `'YYYY-MM-DD HH:MM:SS'' format. The supported range is `'1000-01-01 00:00:00'' to `'9999-12-31 23:59:59''. ("Supported" means that although earlier values might work, they are not guaranteed to.) The `DATE' type is used when you need only a date value, without a time part. *MySQL* retrieves and displays `DATE' values in `'YYYY-MM-DD'' format. The supported range is `'1000-01-01'' to `'9999-12-31''. The `TIMESTAMP' column type provides a type that you can use to automatically mark `INSERT' or `UPDATE' operations with the current time. (`Current time' means `current date and time' in `TIMESTAMP' contexts.) A `TIMESTAMP' column is updated automatically under either of the following conditions: * The column is not specified explicitly in an `INSERT' or `LOAD DATA INFILE' statement. * The column is not specified explicitly in an `UPDATE' statement and some other column changes value. (Note that an `UPDATE' that sets a column to the value it already has will not cause the `TIMESTAMP' column to be updated, because if you set a column to its current value, *MySQL* ignores the update for efficiency.) * You explicitly set the `TIMESTAMP' column to `NULL'. If you have multiple `TIMESTAMP' columns, only the first one is updated automatically. However, you can set any `TIMESTAMP' column to the current time by setting it to `NULL' (or by setting it to `NOW()', obviously). `TIMESTAMP' values may range from the beginning of 1970 to sometime in the year 2106, with a resolution of one second. Values are displayed as numbers. The format in which *MySQL* retrieves and displays `TIMESTAMP' values depends on the display size, as illustrated by the table below. The `full' `TIMESTAMP' format is 14 digits, but `TIMESTAMP' columns may be created with shorter display sizes: *Column type* *Display format* `TIMESTAMP(14)' `YYYYMMDDHHMMSS' `TIMESTAMP(12)' `YYMMDDHHMMSS' `TIMESTAMP(10)' `YYMMDDHHMM' `TIMESTAMP(8)' `YYYYMMDD' `TIMESTAMP(6)' `YYMMDD' `TIMESTAMP(4)' `YYMM' `TIMESTAMP(2)' `YY' All `TIMESTAMP' columns have the same storage size, regardless of display size. The most common display sizes are 6, 8, 12, and 14. (You can specify an arbitrary display size at table creation time, but values of 0 or greater than 14 are coerced to 14. Odd-valued sizes in the range from 1 to 13 are coerced to the next higher even number.) You can specify `DATETIME', `DATE' and `TIMESTAMP' values using any of a common set of formats: * As a string in either `'YYYY-MM-DD HH:MM:SS'' or `'YY-MM-DD HH:MM:SS'' format. A `relaxed' syntax is allowed--any non-numeric character may be used as the delimiter between date parts or time parts. For example, `'98-12-31 11:30:45'', `'98.12.31 11+30+45'', `'98/12/31 11*30*45'' and `'98@12@31 11^30^45'' are equivalent. * As a string in either `'YYYY-MM-DD'' or `'YY-MM-DD'' format. A `relaxed' syntax is allowed here, too. For example, `'98-12-31'', `'98.12.31'', `'98/12/31'' and `'98@12@31'' are equivalent. * As a string with no delimiters in either `'YYYYMMDDHHMMSS'' or `'YYMMDDHHMMSS'' format, provided that the string makes sense as a date. For example, `'19970523091528'' and `'970523091528'' are interpreted as `'1997-05-23 09:15:28'', but `'971122459015'' is illegal (it has a nonsensical minute part) and becomes `'0000-00-00 00:00:00''. * As a string with no delimiters in either `'YYYYMMDD'' or `'YYMMDD'' format, provided that the string makes sense as a date. For example, `'19970523'' and `'970523'' are interpreted as `'1997-05-23'', but `'971332'' is illegal (it has nonsensical month and day parts) and becomes `'0000-00-00''. * As a number in either `YYYYMMDDHHMMSS' or `YYMMDDHHMMSS' format, provided that the number makes sense as a date. For example, `19830905132800' and `830905132800' are interpreted as `'1983-09-05 13:28:00''. * As a number in either `YYYYMMDD' or `YYMMDD' format, provided that the number makes sense as a date. For example, `19830905' and `830905' are interpreted as `'1983-09-05''. * As the result of a function that returns a value that is acceptable in a `DATETIME', `DATE' or `TIMESTAMP' context, such as `NOW()' or `CURRENT_DATE'. For values specified as strings that include date part delimiters, it is not necessary to specify two digits for month or day values that are less than `10'. `'1979-6-9'' is the same as `'1979-06-09''. Similarly, for values specified as strings that include time part delimiters, it is not necessary to specify two digits for hour, month or second values that are less than `10'. `'1979-10-30 1:2:3'' is the same as `'1979-10-30 01:02:03''. Values specified as numbers should be 6, 8, 12 or 14 digits long. If the number is 8 or 14 digits long, it is assumed to be in `YYYYMMDD' or `YYYYMMDDHHMMSS' format and that the year is given by the first 4 digits. If the number is 6 or 12 digits long, it is assumed to be in `YYMMDD' or `YYMMDDHHMMSS' format and that the year is given by the first 2 digits. Numbers that are not one of these lengths are interpreted as though padded with leading zeros to the closest length. Values specified as non-delimited strings are interpreted using their length as given. If the string is 8 or 14 characters long, the year is assumed to be given by the first 4 characters. Otherwise the year is assumed to be given by the first 2 characters. The string is interpreted from left to right to find year, month, day, hour, minute and second values, for as many parts as are present in the string. Year values specified as two digits are ambiguous, since the century is unknown. *MySQL* interprets 2-digit year values using the following rules: * Year values in the range `00-69' are converted to `2000-2069'. * Year values in the range `70-99' are converted to `1970-1999'. You can to some extent assign values of one date type to an object of a different date type. However, there may be some alteration of the value or loss of information: * If you assign a `DATE' value to a `DATETIME' or `TIMESTAMP' object, the time part of the resulting value is set to `'00:00:00'', because the `DATE' value contains no time information. * If you assign a `DATETIME' or `TIMESTAMP' value to a `DATE' object, the time part of the resulting value is deleted, because the `DATE' type stores no time information. `TIMESTAMP' values are stored to full precision regardless of the display size. However, the only function that operates directly on the underlying stored value is `UNIX_TIMESTAMP()'. Other functions operate on the formatted retrieved value. This means you cannot use functions such as `HOUR()' or `SECOND()' unless the relevant part of the `TIMESTAMP' value is included in the formatted value. For example, the `HH' part of a `TIMESTAMP' column is not displayed unless the display size is at least 10, so trying to use `HOUR()' on shorter `TIMESTAMP' values produces a meaningless result. Illegal `DATETIME', `DATE' or `TIMESTAMP' values are converted the `zero' value of the appropriate type (`'0000-00-00 00:00:00'', `'0000-00-00'' or `00000000000000'). Be aware of certain pitfalls when specifying date values: * The relaxed format allowed for values specified as strings can be deceiving. For example, a value such as `'10:11:12'' might look like a time value because of the `:' delimiter, but if used in a date context will be interpreted as the year `'2010-11-12''. The value `'10:45:15'' will be converted to `'0000-00-00'' because `'45'' is not a legal month. * Remember that although `DATETIME', `DATE' and `TIMESTAMP' values all can be specified using the same set of formats, the types do not all have the same range of values. For example, `TIMESTAMP' values cannot be earlier than `1970' or later than `2036'. For example, `'1968-01-01'', while legal as a `DATETIME' or `DATE' value, is not a valid `TIMESTAMP' value and will be converted to `0' if assigned to such an object. The `TIME' type ............... *MySQL* retrieves and displays `TIME' values in `'HH:MM:SS'' format (or `'HHH:MM:SS'' format for large hours values). `TIME' values may range from `'-838:59:59'' to `'838:59:59''. The reason the hours part may be so large is that the `TIME' type may be used not only to represent a time of day (which must be less than 24 hours), but also elapsed time or a time interval between two events (which may be much greater than 24 hours, or even negative). You can specify `TIME' values in a variety of formats: * As a string in `'HH:MM:SS'' format. A `relaxed' syntax is allowed--any non-numeric character may be used as the delimiter between time parts. For example, `'10:11:12'' and `'10.11.12'' are equivalent. * As a string with no delimiters in `'HHMMSS'' format, provided that it makes sense as a time. Example: `'101112'' is understood as `'10:11:12'', but `'109712'' is illegal (it has a nonsensical minute part) and becomes `'00:00:00''. * As a number in `HHMMSS' format, provided that it makes sense as a time. Example: `101112' is understood as `'10:11:12''. * As the result of a function that returns a value that is acceptable in a `TIME' context, such as `CURRENT_TIME'. For `TIME' values specified as strings that include a time part delimiter, it is not necessary to specify two digits for hours, minutes or seconds values that are less than `10'. `'8:3:2'' is the same as `'08:03:02''. If you assign a `short' `TIME' value to a `TIME' column, *MySQL* interprets the value as specifying seconds, or minutes and seconds. For example, `'12'' and `12' are interpreted as `'00:00:12'', whereas `'11:12'', `'1112'' and `1112' are interpreted as `'00:11:12''. Values that lie outside the `TIME' range but are otherwise legal are clipped to the appropriate endpoint of the range. For example, `'-850:00:00'' and `'850:00:00'' are converted to `'-838:59:59'' and `'838:59:59''. Illegal `TIME' values are converted to `'00:00:00''. Note that since `'00:00:00'' is itself a legal `TIME' value, there is no way to distinguish a value of `'00:00:00'' that was specified explicitly from one that resulted from an illegal value. The `YEAR' type ............... The `YEAR' type is a 1-byte type used for representing years. *MySQL* retrieves and displays `YEAR' values in `YYYY' format. The range is `1901' to `2155'. You can specify `YEAR' values in a variety of formats: * As a four-digit string in the range `'1901'' to `'2155''. * As a four-digit number in the range `1901' to `2155'. * As a two-digit string in the range `'00'' to `'99''. Values in the ranges `'00'' to `'69'' and `'70'' to `'99'' are converted to `YEAR' values in the ranges `2000' to `2069' and `1970' to `1999', and are sorted as such. * As a two-digit number in the range `1' to `99'. Values in the ranges `1' to `69' and `70' to `99' are converted to `YEAR' values in the ranges `2001' to `2069' and `1970' to `1999', and are sorted as such. Note that the range for two-digit numbers is slightly different than the range for two-digit strings, since you cannot specify zero directly as a number and have it be interpreted as `2000'. You *must* specify it as a string `'0'' or `'00'' or it will be interpreted as `0000'. * As the result of a function that returns a value that is acceptable in a `YEAR' context, such as `NOW()'. Illegal `YEAR' values are converted to `0000'. String types ------------ The string types are `CHAR', `VARCHAR', `BLOB', `TEXT', `ENUM' and `SET'. The `CHAR' and `VARCHAR' types .............................. The `CHAR' and `VARCHAR' types are similar, but differ in the way they are stored and retrieved. The length of a `CHAR' column is fixed to the length that you declare it when you create the table. You can declare it to be any length between 1 and 255; when values are stored, they are right-padded with spaces to the specified length. When `CHAR' values are retrieved, trailing spaces are removed. Values in `VARCHAR' columns are variable-length strings. You can declare a `VARCHAR' to be any length between 1 and 255 as well. This length is the maximum length, but in contrast to `CHAR', values are stored using only as many characters as are needed. Values are not padded; instead, trailing spaces are removed when values are stored. (This space removal differs from the ANSI SQL specification.) If you assign a value to a `CHAR' or `VARCHAR' column that exceeds the column's maximum length, the value is truncated to fit. To illustrate the differences between the two types of columns, the table below shows the result of storing various string values into `CHAR(4)' and `VARCHAR(4)' columns: *Value* `CHAR(4)' `VARCHAR(4)' `''' `' '' `''' `'ab'' `'ab '' `'ab'' `'abcd'' `'abcd'' `'abcd'' `'abcdef'' `'abcd'' `'abcd'' The values retrieved from the `CHAR(4)' and `VARCHAR(4)' columns will be the same in each case, because trailing spaces are removed from `CHAR' columns upon retrieval. Values in `CHAR' and `VARCHAR' columns are sorted and compared in case-insensitive fashion, unless the `BINARY' attribute was specified when the table was created. The `BINARY' attribute means that column values are sorted and compared in case-sensitive fashion according to the ASCII order of the machine where the *MySQL* server is running. The `BINARY' attribute is "sticky". This means that if a column marked `BINARY' is used in an expression, the whole expression is compared as a `BINARY' value. *MySQL* may silently change the type of a `CHAR' or `VARCHAR' column at table creation time. *Note Create table::. The `BLOB' and `TEXT' types ........................... A `BLOB' is a binary large object that can hold a variable amount of data. The four `BLOB' types `TINYBLOB', `BLOB', `MEDIUMBLOB' and `LONGBLOB' differ only in the maximum length of the values they can hold. The four `TEXT' types `TINYTEXT', `TEXT', `MEDIUMTEXT' and `LONGTEXT' correspond to the four `BLOB' types and have the same maximum lengths and storage requirements. The only difference between `BLOB' and `TEXT' types is that sorting and comparison is performed in case-sensitive fashion for `BLOB' values and case-insensitive fashion for `TEXT' values. In other words, a `TEXT' is a case-insensitive `BLOB'. `BLOB' and `TEXT' columns cannot be indexed, unlike all other *MySQL* column types. If you assign a value to a `BLOB' or `TEXT' column that exceeds the column type's maximum length, the value is truncated to fit. There is no trailing space truncation for `BLOB' and `TEXT' columns as there is for `VARCHAR' columns. In most respects, you can regard a `TEXT' column as a `VARCHAR' column that can be as big as you like. Similarly, you can regard a `BLOB' column as a `VARCHAR BINARY' column. The differences are that you cannot index `BLOB' or `TEXT' columns, and there is no trailing-space removal for `BLOB' and `TEXT' columns when values are stored. `BLOB' and `TEXT' can not have `DEFAULT' values and will also always be `NULL' columns. *MyODBC* defines `BLOB' values as `LONGVARBINARY' and `TEXT' values as `LONGVARCHAR'. Because `BLOB' and `TEXT' values may be extremely long, you may run up against some contraints when using them: * When you sort or group `BLOB' or `TEXT' values, only the first `max_sort_length' bytes of the column are used. The default value of `max_sort_length' is 1024; this value can be changed by the `-O' option when starting the `mysqld' daemon. You can group on an expression involving `BLOB' or `TEXT' values: mysql> SELECT id,substr(blob_col,1,100) GROUP BY 2; * The maximum size of a `BLOB' or `TEXT' object is determined by its type, but the largest value you can actually transmit between the client and server is determined by the amount of available memory and the size of the communications buffers. You can change the message buffer size, but you must do so on both the server and client ends. *Note *MySQL* parameters: MySQL parameters. Note that each `BLOB/TEXT' column is represented internally by a unique alloced object. This is in contrast to all other column types that are alloced once when the table is opened. The `ENUM' type ............... An `ENUM' (enumeration) is a string object that can have only one value, chosen from a list of allowed values, or `NULL'. For example, a column specified as `ENUM("one", "two", "three")' can have any of these values: NULL "one" "two" "three" An enumeration can have a maximum of 65535 elements. When you assign a value to an `ENUM' column, the case of the value to be stored does not matter; the stored value is converted to the case that was used to specify the `ENUM' column when the table was created. If you retrieve an `ENUM' in a numeric context, the column value's index is returned. If you store a number into an `ENUM', the value stored is the enumeration member whose index is that number. Enumeration values are indexed beginning with 1 (0 is reserved for incorrect enumeration values). Sorting of `ENUM' values is done according to the order in which the enumeration members were listed in the column specification. For example, `"a"' sorts before `"b"' for `ENUM("a", "b")', but `"a"' sorts after `"b"' for `ENUM("b", "a")'. `NULL' values sort before other enumeration values. If an `ENUM' is declared `NOT NULL', the default value is the first value, otherwise the default value is `NULL'. The `SET' type .............. A `SET' is a string object that can have zero or more values, each of which must be chosen from a list of allowed values. `SET' column values that are composed of multiple set members are specified with members separated by commas (`,'). For example, a column specified as `SET("one", "two") NOT NULL' can have any of these values: "" "one" "two" "one,two" A `SET' can have a maximum of 64 different members. *MySQL* stores `SET' values numerically, with the low-order bit of the stored value corresponding to the first set member. If you retrieve a set value into a numeric context, the value retrieved has the bit (or bits) set corresponding to the set member (or members) that make up the column value. If a number is stored into a `SET' column, the bit (or bits) that are set in the number determine the set member (or members) in the column value. Sorting of `SET' values is done numerically. `NULL' values sort before other set members. Normally, you perform a `SELECT' on a `SET' column using `LIKE' or `FIND_IN_SET()': mysql> SELECT * FROM tbl_name WHERE set_col LIKE '%value%'; mysql> SELECT * FROM tbl_name WHERE FIND_IN_SET('value',set_col)>0; But the following will also work: mysql> SELECT * FROM tbl_name WHERE set_col = 'val1,val2'; # Exact match mysql> SELECT * FROM tbl_name WHERE set_col & 1; # Is in first group Choosing the right type for a column ------------------------------------ Try to use the most precise type in all cases. For example, if an integer column will be used for values in the range between `1' and `99999', `MEDIUMINT UNSIGNED' is the best type. Accurate representation of monetary values is a common problem. In *MySQL* you should use the `DECIMAL' type. This is stored as a string, so no loss of accuracy should occur. If accuracy is not too important, the `DOUBLE' type may also be good enough. For high precision, you can always convert to a fixed-point type stored in a `BIGINT'. This allows you to do all calculations with integers and convert results back to floating-point values only when necessary. *Note Row format::. Column indexes -------------- All *MySQL* column types can be indexed except `BLOB' and `TEXT' types. Use of indexes on the relevant columns is the best way to improve the performance of `SELECT' operations. A table may have up to 16 indexes. The maximum index length is 256 bytes, although this may be changed when compiling *MySQL*. For `CHAR' and `VARCHAR' columns, you can index a prefix of a column. This is much faster and requires less disk space than indexing the whole column. The syntax to use in the `CREATE TABLE' statement to index a column prefix looks like this: KEY index_name (col_name(length)) The example below creates an index for the first 10 characters of the `name' column: mysql> CREATE TABLE test ( name CHAR(200) NOT NULL, KEY index_name (name(10))); Multiple-column indexes ----------------------- *MySQL* can create indexes from multiple columns. A multiple-column index can be considered a sorted array where the values of the indexed columns are concatenated. *MySQL* uses multiple-column indexes in such a way that queries are fast when you specify a known quantity for the first column of the index in a `WHERE' clause, even if you don't specify values for the other columns. An index may consist up up to 15 columns (or column prefixes, for `CHAR' and `VARCHAR' columns). Suppose you have a table that has the following specification: mysql> CREATE TABLE test ( id INT NOT NULL, last_name CHAR(30) NOT NULL, first_name CHAR(30) NOT NULL, PRIMARY KEY (id), INDEX name (last_name,first_name)); Then the index `name' is an index over `last_name' and `first_name'. The index will be used for queries that specify values in a known range for `last_name', or for both `last_name' and `first_name'. Therefore, the `name' index will be used in the following queries: mysql> SELECT * FROM test WHERE last_name="Widenius"; mysql> SELECT * FROM test WHERE last_name="Widenius" AND first_name="Michael"; mysql> SELECT * FROM test WHERE last_name="Widenius" AND (first_name="Michael" OR first_name="Monty"); mysql> SELECT * FROM test WHERE last_name="Widenius" AND first_name >="M" AND first_name < "N"; However, the `name' index will NOT be used in the following queries: mysql> SELECT * FROM test WHERE first_name="Michael"; mysql> SELECT * FROM test WHERE last_name="Widenius" or first_name="Michael"; For more information on the manner in which *MySQL* uses indexes to improve query performance, see *Note *MySQL* indexes: MySQL indexes. Using column types from other database engines ---------------------------------------------- To make it easier to use code written for SQL implementations from other vendors, *MySQL* supports the column type mappings shown in the table below. These mappings make it easier to move table definitions from other database engines to *MySQL*: *Other vendor type* *MySQL type* `BINARY(NUM)' `CHAR(NUM) BINARY' `CHAR VARYING(NUM)' `VARCHAR(NUM)' `FLOAT4' `FLOAT' `FLOAT8' `DOUBLE' `INT1' `TINYINT' `INT2' `SMALLINT' `INT3' `MEDIUMINT' `INT4' `INT' `INT8' `BIGINT' `LONG VARBINARY' `MEDIUMBLOB' `LONG VARCHAR' `MEDIUMTEXT' `MIDDLEINT' `MEDIUMINT' `VARBINARY(NUM)' `VARCHAR(NUM) BINARY' Column type mapping occurs at table creation time, so if you create a table with types used by other vendors and then issue a `DESCRIBE tbl_name' statement, *MySQL* reports the table structure using the equivalent *MySQL* types. Functions for use in `SELECT' and `WHERE' clauses ================================================= A `select_expression' or `where_definition' can consist of any expression using the functions described below. An expression that contains `NULL' always produces a `NULL' value unless otherwise indicated in the documentation for the operators and functions involved in the expression. *Note:* there must be no whitespace between a function name and the parenthesis following it. This helps the *MySQL* parser distinguish between function calls and references to tables or columns that happen to have the same name as a function. For the sake of brevity, the examples shown below display the output from the `mysql' program in abbreviated form. So this: mysql> select MOD(29,9); 1 rows in set (0.00 sec) +-----------+ | mod(29,9) | +-----------+ | 2 | +-----------+ Is displayed like this: mysql> select MOD(29,9); -> 2 Grouping functions ------------------ `( ... )' Parentheses. Use these to force the order of evaluation in an expression. mysql> select 1+2*3; -> 7 mysql> select (1+2)*3; -> 9 Normal arithmetic operations ---------------------------- Note that in the case of `-', `+' and `*', the result is calculated with `BIGINT' precision if both arguments are integers! `+' Addition mysql> select 3+5; -> 8 `-' Subtraction mysql> select 3-5; -> -2 `*' Multiplication mysql> select 3*5; -> 15 mysql> select 18014398509481984*18014398509481984.0; -> 324518553658426726783156020576256.0 mysql> select 18014398509481984*18014398509481984; -> 0 The result of the last expression is incorrect because the result of the integer multiplication is over the 64-bit range. `/' Division. A division by zero produces a `NULL' result. mysql> select 3/5; -> 0.60 mysql> select 102/(1-1); -> NULL A division will be calculated with `BIGINT' arithmetic only if it's used in a context where its result is converted to an integer! Bit functions ------------- These have a maximum range of 64 bits because *MySQL* uses `BIGINT' (64-bit) arithmetic for bit operations. `|' Bitwise OR mysql> select 29 | 15; -> 31 `&' Bitwise AND mysql> select 29 & 15; -> 13 `<<' Shifts a longlong number to the left. mysql> select 1 << 2 -> 4 `>>' Shifts a longlong number to the right. mysql> select 4 >> 2 -> 1 `BIT_COUNT(N)' Returns the number of bits that are set in the argument `N'. mysql> select BIT_COUNT(29); -> 4 Logical operations ------------------ All logical functions return `1' (TRUE) or `0' (FALSE). `NOT' `!' Logical NOT. Returns `1' if the argument is `0', otherwise returns `0'. Exception: `NOT NULL' returns `NULL'. mysql> select NOT 1; -> 0 mysql> select NOT NULL; -> NULL mysql> select ! (1+1); -> 0 mysql> select ! 1+1; -> 1 The last example returns `1' because the expression evaluates the same way as `(!1)+1'. `OR' `||' Logical OR. Returns `1' if either argument is not `0' and not `NULL'. mysql> select 1 || 0; -> 1 mysql> select 0 || 0; -> 0 mysql> select 1 || NULL; -> 1 `AND' `&&' Logical AND. Returns `0' if either argument is `0' or `NULL', otherwise returns `1'. mysql> select 1 && NULL; -> 0 mysql> select 1 && 0; -> 0 Comparison operators -------------------- Comparison operations result in a value of `1' (TRUE), `0' (FALSE) or `NULL'. These functions work for both numbers and strings. Strings are automatically converted to numbers and numbers to strings as needed (as in Perl). *MySQL* performs comparisons using the following rules: * If one or both arguments are `NULL', the result of the comparison is `NULL'. * If both arguments in a comparison operation are strings, they are compared as strings. * If both arguments are integers, they are compared as integers. * If one of the arguments is a `TIMESTAMP' or `DATETIME' column and the other argument is a constant, the constant is converted to a timestamp before the comparison is performed. This is done to be more ODBC-friendly. * In all other cases, the arguments are compared as floating-point (real) numbers. By default, string comparisons are done in case-independent fashion using the current character set (ISO-8859-1 Latin1 by default, which also works excellently for English). The examples below illustrate conversion of strings to numbers for comparison operations: mysql> SELECT 1 > '6x'; -> 0 mysql> SELECT 7 > '6x'; -> 1 mysql> SELECT 0 > 'x6'; -> 0 mysql> SELECT 0 = 'x6'; -> 1 `=' Equal mysql> select 1 = 0; -> 0 mysql> select '0' = 0; -> 1 mysql> select '0.0' = 0; -> 1 mysql> select '0.01' = 0; -> 0 mysql> select '.01' = 0.01; -> 1 `<>' `!=' Not equal mysql> select '.01' <> '0.01'; -> 1 mysql> select .01 <> '0.01'; -> 0 mysql> select 'zapp' <> 'zappp'; -> 1 `<=' Less than or equal mysql> select 0.1 <= 2; -> 1 `<' Less than mysql> select 2 <= 2; -> 1 `>=' Greater than or equal mysql> select 2 >= 2; -> 1 `>' Greater than mysql> select 2 > 2; -> 0 `ISNULL(expr)' If `expr' is `NULL', returns `1', otherwise returns `0'. mysql> select ISNULL(1+1); -> 0 mysql> select ISNULL(1/0); -> 1 `expr BETWEEN min AND max' If `expr' is greater than or equal to `min' and `expr' is less than or equal to `max', returns `1', otherwise returns `0'. Does the same thing as the expression `(min <= expr AND expr <= max)' if all the arguments are of the same type. The first argument (`expr') determines how the comparison is performed. If `expr' is a string expression, a case-insensitive string comparison is done. If `expr' is a binary string, a case-sensitive string comparison is done. If `expr' is an integer expression, an integer comparison is done. Otherwise, a floating-point (real) comparison is done. mysql> select 1 BETWEEN 2 AND 3; -> 0 mysql> select 'b' BETWEEN 'a' AND 'c'; -> 1 mysql> select 2 BETWEEN 2 AND '3'; -> 1 mysql> select 2 BETWEEN 2 AND 'x-3'; -> 0 `expr IN (value,...)' Returns `1' if `expr' is any of the values in the `IN' list, else returns `0'. If all values are constants, then all values are evaluated according to the type of `expr' and sorted. The search for the item is then done using a binary search. This means `IN' is very quick when used with constants in the `IN' value list. If `expr' is a case-sensitive string expression, the string comparison is done in case-sensitive fashion. mysql> select 2 IN (0,3,5,'wefwf'); -> 0 mysql> select 'wefwf' IN (0,3,5,'wefwf'); -> 1 `expr NOT IN (value,...)' Same as `NOT (expr IN (value,...))'. `INTERVAL(N,N1,N2,N3...)' Returns `0' if `N' < `N1', `1' if `N' < `N2' and so on. All arguments are treated as numbers. It is required that `N1' < `N2' < `N3' < `Nn' for this function to work correctly. This is because a binary search is used (very fast). mysql> select INTERVAL(23, 1, 15, 17, 30, 44, 200); -> 3 mysql> select INTERVAL(10, 1, 10, 100, 1000); -> 2 mysql> select INTERVAL(22, 23, 30, 44, 200); -> 0 String comparison functions --------------------------- Normally, if one expression to be compared is not case sensitive, string comparisons are done in case-insensitive fashion. `expr1 LIKE expr2 [ESCAPE string-of-one-character]' SQL simple regular expression comparison. Returns `1' (TRUE) or `0' (FALSE). With `LIKE' you can use the following two wildcard characters: `%' Matches any number of characters, even zero characters `_' Matches exactly one character If one doesn't specify the `ESCAPE' character `'\'' will be used. To test for literal instances of the wildcard characters, use the following sequences: `\%' Matches one `%' character `\_' Matches one `_' character mysql> select 'David!' LIKE 'David_'; -> 1 mysql> select 'David!' LIKE 'David\_'; -> 0 mysql> select 'David_' LIKE 'David\_'; -> 1 mysql> select 'David!' LIKE '%D%v%'; -> 1 mysql> select 10 LIKE '1%'; -> 1 mysql> select 'David_' LIKE 'David|_' ESCAPE '|' `LIKE' is allowed on numeric expressions! (This is a *MySQL* extension to the ANSI SQL `LIKE'.) `expr1 NOT LIKE expr2 [ESCAPE 'string-of-one-character']' Same as `NOT (expr1 LIKE expr2 [ESCAPE 'string-of-one-character'])'. `expr REGEXP pat' `expr RLIKE pat' Performs a pattern match of a string expression `expr' against a pattern `pat'. The pattern can be an extended regular expression. *Note Regexp::. Returns `1' if `expr' matches `pat', otherwise returns `0'. `RLIKE' is a synonym for `REGEXP', provided for `mSQL' compatibility. NOTE: Because *MySQL* uses the C escape syntax in strings (`\n'), you must double any `'\'' that you use in your `REGEXP' strings. mysql> select 'Monty!' REGEXP 'm%y%%'; -> 0 mysql> select 'Monty!' REGEXP '.*'; -> 1 mysql> select 'new*\n*line' REGEXP 'new\\*.\\*line'; -> 1 `' `REGEXP' and `RLIKE' use the current character set (ISO-8859-1 Latin1 by default) when deciding the type of a character. `expr NOT REGEXP expr' Same as `NOT (expr REGEXP expr)'. `STRCMP(expr1,expr2)' Returns `0' if the strings are the same. Returns `-1' if the first argument is smaller than the second according to the current sort order. Otherwise returns `1'. mysql> select STRCMP('text', 'text2'); -> -1 mysql> select STRCMP('text2', 'text'); -> 1 mysql> select STRCMP('text', 'text'); -> 0 Control flow functions ---------------------- `IFNULL(expr1,expr2)' If `expr1' is not `NULL', `IFNULL()' returns `expr1', else returns `expr2'. `IFNULL()' returns a numeric or string value, depending on the context in which it are used. mysql> select IFNULL(1,0); -> 1 mysql> select IFNULL(0,10); -> 0 mysql> select IFNULL(1/0,10); -> 10 mysql> select IFNULL(1/0,'yes'); -> 'yes' `IF(expr1,expr2,expr3)' If `expr1' is TRUE (`expr1 <> 0' and `expr1 <> NULL') then returns `expr2', else returns `expr3'. `IFNULL()' returns a numeric or string value, depending on the context in which it are used. `expr1' is evaluated as an `INTEGER', which means that if you are testing floating-point values, you should do so using a comparison operation. mysql> select IF(1>2,2,3); -> 3 mysql> select IF(1<2,'yes','no'); -> 'yes' mysql> select IF(strcmp('test','test1'),'yes','no'); -> 'no' mysql> select IF(0.1<>0,1,0); -> 1 mysql> select IF(0.1,1,0); -> 0 Mathematical functions ---------------------- All mathematical functions return `NULL' in case of an error. `-' Sign. Changes the sign of the argument. mysql> select - 2; -> -2 Note that if this function is used with a `BIGINT', the return value is a `BIGINT'! This means that you should avoid using `-' on integers that may have the value of -2^63 ! `ABS(X)' Returns the absolute value of `X'. mysql> select ABS(2); -> 2 mysql> select ABS(-32); -> 32 This function is safe to use with `BIGINT' values. `SIGN(X)' Returns the sign of the argument (`-1', `0' or `1', depending on whether `X' is negative, zero, or positive). mysql> select SIGN(-32); -> -1 mysql> select SIGN(0); -> 0 mysql> select SIGN(234); -> 1 `MOD(N,M)' `%' Modulo (like `%' in C). Returns the remainder of `N' divided by `M'. mysql> select MOD(234, 10); -> 4 mysql> select 253 % 7; -> 1 mysql> select MOD(29,9); -> 2 This function is safe to use with `BIGINT' values. `FLOOR(X)' Returns the largest integer value not greater than `X'. mysql> select FLOOR(1.23); -> 1 mysql> select FLOOR(-1.23); -> -2 Note that the return value is converted to a `BIGINT' ! `CEILING(X)' Returns the smallest integer value not less than `X'. mysql> select CEILING(1.23); -> 2 mysql> select CEILING(-1.23); -> -1 Note that the return value is converted to a `BIGINT' ! `ROUND(X)' Returns the argument `X', rounded to an integer. mysql> select ROUND(-1.23); -> -1 mysql> select ROUND(-1.58); -> -2 mysql> select ROUND(1.58); -> 2 Note that the return value is converted to a `BIGINT' ! `ROUND(X,D)' Returns the argument `X', rounded to a number with `D' decimals. mysql> select ROUND(1.298, 1); -> 1.3 Note that the return value is converted to a `BIGINT' ! `EXP(X)' Returns the value of `e' (the base of natural logarithms) raised to the power of `X'. mysql> select EXP(2); -> 7.389056 mysql> select EXP(-2); -> 0.135335 `LOG(X)' Returns the natural logarithm of `X'. mysql> select LOG(2); -> 0.693147 mysql> select LOG(-2); -> NULL If you want the log of a number `X' to some arbitary base `B', use the formula `LOG(X)/LOG(B)'. `LOG10(X)' Returns the base-10 logarithm of `X'. mysql> select LOG10(2); -> 0.301030 mysql> select LOG10(100); -> 2.000000 mysql> select LOG10(-100); -> NULL `POW(X,Y)' `POWER(X,Y)' Returns the value of `X' raised to the power of `Y'. mysql> select POW(2,2); -> 4.000000 mysql> select POW(2,-2); -> 0.250000 `SQRT(X)' Returns the non-negative square root of `X'. mysql> select SQRT(4); -> 2.000000 mysql> select SQRT(20); -> 4.472136 `PI()' Returns the value of PI. mysql> select PI(); -> 3.141593 `COS(X)' Returns the cosine of `X', where `X' is given in radians. mysql> select COS(PI()); -> -1.000000 `SIN(X)' Returns the sine of `X', where `X' is given in radians. mysql> select SIN(PI()); -> 0.000000 `TAN(X)' Returns the tangent of `X', where `X' is given in radians. mysql> select TAN(PI()+1); -> 1.557408 `ACOS(X)' Returns the arc cosine of `X', that is, the value whose cosine is `X'. Returns `NULL' if `X' is not in the range -1 to 1. mysql> select ACOS(1); -> 0.000000 mysql> select ACOS(1.0001); -> NULL mysql> select ACOS(0); -> 1.570796 `ASIN(X)' Returns the arc sine of `X', that is, the value whose sine is `X'. Returns `NULL' if `X' is not in the range -1 to 1. mysql> select ASIN(0.2); -> 0.201358 mysql> select ASIN('foo'); -> 0.000000 `ATAN(X)' Returns the arc tangent of `X', that is, the value whose tangent is `X'. mysql> select ATAN(2); -> 1.107149 mysql> select ATAN(-2); -> -1.107149 `ATAN2(X,Y)' Returns the arc tangent of the two variables `X' and `Y'. It is similar to calculating the arc tangent of `Y / X', except that the signs of both arguments are used to determine the quadrant of the result. mysql> select ATAN(-2,2); -> -0.785398 mysql> select ATAN(PI(),0); -> 1.570796 `COT(X)' Returns the cotangent of `X'. mysql> select COT(12); -> -1.57267341 mysql> select COT(0); -> NULL `RAND()' `RAND(N)' Returns a random floating-point value in the range `0' to `1.0'. If an integer argument `N' is specified, it is used as the seed value. mysql> select RAND(); -> 0.5925 mysql> select RAND(20); -> 0.1811 mysql> select RAND(20); -> 0.1811 mysql> select RAND(); -> 0.2079 mysql> select RAND(); -> 0.7888 You can't do an `ORDER BY' on a column with `RAND()' values because `ORDER BY' would evaluate the column multiple times. `LEAST(X,Y...)' With two or more arguments, returns the smallest (minimum-valued) argument. The arguments are compared according to the following rules: * If the value is used as an `INTEGER', or all arguments are integer-valued, then they are compared as integers. * If the value is used as a `REAL', or all arguments are real-valued, then they are compared as reals. * If any argument is a case-sensitive string, then the arguments are compared as case-sensitive strings * In other cases, the arguments are compared as case-insensitive strings. mysql> select LEAST(2,0); -> 0 mysql> select LEAST(34.0,3.0,5.0,767.0); -> 3.0 mysql> select LEAST("B","A","C"); -> "A" In *MySQL* versions prior to 3.22.5, you can use `MIN()' instead of `LEAST'. `GREATEST(X,Y...)' Returns the largest (maximum-valued) argument. The arguments are compared according to the same rules as for `LEAST'. mysql> select GREATEST(2,0); -> 2 mysql> select GREATEST(34.0,3.0,5.0,767.0); -> 767.0 mysql> select GREATEST("B","A","C"); -> "C" In *MySQL* versions prior to 3.22.5, you can use `MAX()' instead of `GREATEST'. `DEGREES(X)' Returns the argument `X', converted from radians to degrees. mysql> select DEGREES(PI()); -> 180.000000 `RADIANS(X)' Returns the argument `X', converted from degrees to radians. mysql> select RADIANS(90); -> 1.570796 `TRUNCATE(X,D)' Returns the number `X', truncated to `D' decimals. mysql> select TRUNCATE(1.223,1); -> 1.2 mysql> select TRUNCATE(1.999,1); -> 1.9 mysql> select TRUNCATE(1.999,0); -> 1 String functions ---------------- For functions that operate on string positions, the first position is numbered 1. `ASCII(str)' Returns the ASCII code value of the leftmost character of the string `str'. Returns `0' if `str' is the empty string. Returns `NULL' if `str' is `NULL'. mysql> select ASCII(2); -> 50 mysql> select ASCII('dx'); -> 100 `CONV(N,FROM_BASE,TO_BASE)' Converts numbers between different number bases. Returns a string representation of the number `N', converted from base `FROM_BASE' to base `TO_BASE'. Returns `NULL' if any argument is `NULL'. The argument `N' is interpreted as an integer, but may be specified as an integer or a string. The minimum base is `2' and the maximum base is `36'. If `TO_BASE' is a negative number, `N' is regarded as a signed number. `CONV' works with 64-bit precision. mysql> select CONV("a",16,2); -> '1010' mysql> select CONV("6E",18,8); -> '172' mysql> select CONV(-17,10,-18); -> '-H' mysql> select CONV(10+"10"+'10'+0xa,10,10); -> '40' `BIN(N)' Returns a string representation of the binary value of `N' where `N' is a longlong number. This is the same as `CONV(N,10,2)'. Returns `NULL' if `N' is `NULL'. mysql> select BIN(12); -> '1100' `OCT(N)' Returns a string representation of the octal value of `N' where `N' is a longlong number. This is the same as `CONV(N,10,8)'. Returns `NULL' if `N' is `NULL'. mysql> select OCT(12); -> '14' `HEX(N)' Returns a string representation of the hexadecimal value of `N' where `N' is a longlong number. This is the same as `CONV(N,10,16)'. Returns `NULL' if `N' is `NULL'. mysql> select HEX(255); -> 'FF' `CHAR(N,...)' Returns a string consisting of the characters given by the ASCII code values of the arguments. `NULL' values are skipped. mysql> select CHAR(77,121,83,81,'76'); -> 'MySQL' `CONCAT(X,Y...)' Returns the string that results from concatenating the arguments. Returns `NULL' if any argument is `NULL'. May have more than 2 arguments. mysql> select CONCAT('My', 'S', 'QL'); -> 'MySQL' mysql> select CONCAT('My', NULL, 'QL'); -> NULL `LENGTH(str)' `OCTET_LENGTH(str)' `CHAR_LENGTH(str)' `CHARACTER_LENGTH(str)' Returns the length of the string `str'. mysql> select LENGTH('text'); -> 4 mysql> select OCTET_LENGTH('text'); -> 4 `LOCATE(substr,str)' `POSITION(substr IN str)' Returns the position of the first occurrence of substring `substr' in string `str'. Returns `0' if `substr' is not in `str'. mysql> select LOCATE('bar', 'foobarbar'); -> 4 mysql> select LOCATE('xbar', 'foobar'); -> 0 `LOCATE(substr,str,pos)' Returns the position of the first occurrence of substring `substr' in string `str', starting at position `pos'. Returns `0' if `substr' is not in `str'. mysql> select LOCATE('bar', 'foobarbar',5); -> 7 `INSTR(str,substr)' Returns the position of the first occurrence of substring `substr' in string `str'. This is the same as the two-argument form of `LOCATE', except that the arguments are swapped. mysql> select INSTR('foobarbar', 'bar'); -> 4 mysql> select INSTR('xbar', 'foobar'); -> 0 `LPAD(str,len,padstr)' Returns the string `str', left-padded with the string `padstr' until `str' is `len' characters long. mysql> select LPAD('hi',4,'??'); -> '??hi' `RPAD(str,len,padstr)' Returns the string `str', right-padded with the string `padstr' until `str' is `len' characters long. mysql> select RPAD('hi',5,'?'); -> 'hi???' `LEFT(str,len)' Returns the leftmost `len' characters from the string `str'. mysql> select LEFT('foobarbar', 5); -> 'fooba' `RIGHT(str,len)' `SUBSTRING(str FROM len)' Returns the rightmost `len' characters from the string `str'. mysql> select RIGHT('foobarbar', 4); -> 'rbar' mysql> select SUBSTRING('foobarbar' from 4); -> 'rbar' `SUBSTRING(str,pos,len)' `SUBSTRING(str FROM pos FOR len)' `MID(str,pos,len)' Returns a substring `len' characters long from string `str', starting at position `pos'. The variant form that uses `FROM' is ANSI SQL 92 syntax. mysql> select SUBSTRING('Quadratically',5,6); -> 'ratica' `SUBSTRING(str,pos)' Returns a substring from string `str' starting at position `pos'. mysql> select SUBSTRING('Quadratically',5); -> 'ratically' `SUBSTRING_INDEX(str,delim,count)' Returns the substring from string `str' after `count' occurrences of the delimiter `delim'. If `count' is positive, everything to the left of the final delimiter (counting from the left) is returned. If `count' is negative, everything to the right of the final delimiter (counting from the right) is returned. mysql> select SUBSTRING_INDEX('www.tcx.se', '.', 2); -> 'www.tcx' mysql> select SUBSTRING_INDEX('www.tcx.se', '.', -2); -> 'tcx.se' `LTRIM(str)' Returns the string `str' with leading space characters removed. mysql> select LTRIM(' barbar'); -> 'barbar' `RTRIM(str)' Returns the string `str' with trailing space characters removed. mysql> select RTRIM('barbar '); -> 'barbar' `TRIM([[BOTH | LEADING | TRAILING] [remstr] FROM] str)' Returns the string `str' with all `remstr' prefixes and/or suffixes removed. If none of the specifiers `BOTH', `LEADING' or `TRAILING' are given, `BOTH' is assumed. If `remstr' is not specified, spaces are removed. mysql> select TRIM(' bar '); -> 'bar' mysql> select TRIM(leading 'x' from 'xxxbarxxx'); -> 'barxxx' mysql> select TRIM(both 'x' from 'xxxbarxxx'); -> 'bar' mysql> select TRIM(trailing 'xyz' from 'barxxyz'); -> 'barx' `SOUNDEX(str)' Returns a soundex string from `str'. Two strings that sound "about the same" should have identical soundex strings. A "standard" soundex string is 4 characters long, but the `SOUNDEX()' function returns an arbitrarily long string. You can use `SUBSTRING()' on the result to get a "standard" soundex string. All non-alpha characters are ignored in the given string. All characters outside the A-Z range are treated as vowels. mysql> select SOUNDEX('Hello'); -> 'H400' mysql> select SOUNDEX('Quadratically'); -> 'Q36324' `SPACE(N)' Returns a string consisting of `N' space characters. mysql> select SPACE(6); -> ' ' `REPLACE(str,from,to)' Returns the string `str' with all all occurrences of the string `from' replaced by the string `to'. mysql> select REPLACE('www.tcx.se', 'w', 'Ww'); -> 'WwWwWw.tcx.se' `REPEAT(str,count)' Returns a string consisting of the string `str' repeated `count' times. If `count <= 0', returns an empty string. Returns `NULL' if `str' or `count' are `NULL' or if `LENGTH(str)*count > max_allowed_packet'. mysql> select REPEAT('MySQL', 3); -> 'MySQLMySQLMySQL' `REVERSE(str)' Returns the string `str' with the order of the characters reversed. mysql> select REVERSE('abc'); -> 'cba' `INSERT(str,start,len,newstr)' Returns the string `str', with the substring beginning at position `start' and `len' characters long replaced by the string `newstr'. mysql> select INSERT('Quadratic', 3, 4, 'What'); -> 'QuWhattic' `ELT(N,str1,str2,str3...)' Returns `str1' if `N' = 1, `str2' if `N' = 2, and so on. Returns `NULL' if `N' is less than 1 or greater than the number of arguments. `ELT()' is the complement of `FIELD()'. mysql> select ELT(1, 'ej', 'Heja', 'hej', 'foo'); -> 'ej' mysql> select ELT(4, 'ej', 'Heja', 'hej', 'foo'); -> 'foo' `FIELD(str,str1,str2,str3...)' Returns the index of `str' in the `str1', `str2', `str3'... list. Returns `0' if `str' is not found. `FIELD()' is the complement of `ELT()'. mysql> select FIELD('ej', 'Hej', 'ej', 'Heja', 'hej', 'foo'); -> 2 mysql> select FIELD('fo', 'Hej', 'ej', 'Heja', 'hej', 'foo'); -> 0 `FIND_IN_SET(str,strlist)' Returns a value `1' to `N' if the string `str' is in the list `strlist' consisting of `N' substrings. A string list is itself a string with its individual substrings separated by ',' characters. If the first argument is a constant string and the second is a column of type `SET', the `FIND_IN_SET' is optimized to use bit arithmetic! Returns `0' if `strlist' is the empty string. Returns `NULL' if either argument is `NULL'. This function will not work properly if the first argument contains a ','. mysql> SELECT FIND_IN_SET('b','a,b,c,d'); -> 2 `MAKE_SET(bits,strlist)' Returns a set (a string separated with `,') of the strings that have the corresponding bit set. `NULL' strings in the set list are not appended to the result. mysql> SELECT MAKE_SET(1,'a','b','c'); -> 'a' mysql> SELECT MAKE_SET(1 | 4,'hello','nice','world'); -> 'hello,world' mysql> SELECT MAKE_SET(0,'a','b','c'); -> '' `LCASE(str)' `LOWER(str)' Returns the string `str' with all characters changed to lowercase according to the current character set mapping (the default is Latin1). mysql> select LCASE('QUADRATICALLY'); -> 'quadratically' `UCASE(str)' `UPPER(str)' Returns the string `str' with all characters changed to uppercase according to the current character set mapping (the default is Latin1). mysql> select UCASE('Hej'); -> 'HEJ' There is no string function to convert a number to a char. This is not needed as MySQL automaticly converts numbers to string and vice versa: SELECT 1+"1"; -> 2 SELECT concat(2,' test'); -> '2 test' If a string function gets a binary string as an argument, the resulting string is also a binary string. A number converted to a string is treated as a binary string. This only affects comparisons. Date and time functions ----------------------- Here is an example that uses date functions. The query below selects all records with a `date_field' value from the last 30 days: mysql> SELECT something FROM table WHERE TO_DAYS(NOW()) - TO_DAYS(date_field) <= 30; See *Note Date and time types:: for a description of the range of values each type has, and the valid formats in which date and time values may be specified. `DAYOFWEEK(date)' Returns the weekday index for `date' (`1' = Sunday, `2' = Monday, ... `7' = Saturday). These index values correspond to the ODBC standard. mysql> select DAYOFWEEK('1998-02-03'); -> 3 `WEEKDAY(date)' Returns the weekday index for `date' (`0' = Monday, `1' = Tuesday, ... `6' = Sunday). mysql> select WEEKDAY('1997-10-04 22:23:00'); -> 5 mysql> select WEEKDAY('1997-11-05'); -> 2 `DAYOFMONTH(date)' Returns the day of the month for `date', in the range `1' to `31'. mysql> select DAYOFMONTH('1998-02-03'); -> 3 `DAYOFYEAR(date)' Returns the day of the year for `date', in the range `1' to `366'. mysql> select DAYOFYEAR('1998-02-03'); -> 34 `MONTH(date)' Returns the month for `date', in the range `1' to `12'. mysql> select MONTH('1998-02-03'); -> 2 `DAYNAME(date)' Returns the name of the weekday for `date'. mysql> select DAYNAME("1998-02-05"); -> Thursday `MONTHNAME(date)' Returns the name of the month for `date'. mysql> select MONTHNAME("1998-02-05"); -> February `QUARTER(date)' Returns the quarter of the year for `date', in the range `1' to `4'. mysql> select QUARTER('98-04-01'); -> 2 `WEEK(date)' `WEEK(date,first)' With a single argument, returns the week for `date', in the range `0' to `52', for locations where Sunday is the first day of the week. The two-argument form of `WEEK()' allows you to specify whether the week starts on Sunday or Monday. The week starts on Sunday if the second argument is `0', on Monday if the second argument is `1'. mysql> select WEEK('1998-02-20'); -> 7 mysql> select WEEK('1998-02-20',0); -> 7 mysql> select WEEK('1998-02-20',1); -> 8 `YEAR(date)' Returns the year for `date', in the range `1000' to `9999'. mysql> select YEAR('98-02-03'); -> 1998 `HOUR(time)' Returns the hour for `time', in the range `0' to `23'. mysql> select HOUR('10:05:03'); -> 10 `MINUTE(time)' Returns the minute for `time', in the range `0' to `59'. mysql> select MINUTE('98-02-03 10:05:03'); -> 5 `SECOND(time)' Returns the second for `time', in the range `0' to `59'. mysql> select SECOND('10:05:03'); -> 3 `PERIOD_ADD(P,N)' Adds `N' months to period `P' (in the format `YYMM' or `YYYYMM'). Returns a value in the format `YYYYMM'. mysql> select PERIOD_ADD(9801,2); -> 199803 `PERIOD_DIFF(P1,P2)' Returns the number of months between periods `P1' and `P2'. `P1' and `P2' should be in the format `YYMM' or `YYYYMM'. mysql> select PERIOD_DIFF(9802,199703); -> 11 `DATE_ADD(date,INTERVAL expr type)' `DATE_SUB(date,INTERVAL expr type)' `ADDDATE(date,INTERVAL expr type)' `SUBDATE(date,INTERVAL expr type)' These functions perform date arithmetic. They are new for *MySQL* 3.22. `ADDDATE()' and `SUBDATE()' are synonyms for `DATE_ADD()' and `DATE_SUB()'. `date' is the starting date (a `DATETIME' or `DATE' value). `expr' is an expression specifying the interval value to be added or substracted from the starting date. `expr' is a string; it may start with a `-' for negative intervals. `type' is an interval type keyword indicating how the expression should be interpreted. `type' *Meaning* `expr' *format* *value* `SECOND' Seconds `SECONDS' `MINUTE' Minutes `MINUTES' `HOUR' Hours `HOURS' `DAY' Days `DAYS' `MONTH' Months `MINUTES' `YEAR' Years `YEARS' `MINUTE_SECOND'Minutes and seconds `"MINUTES:SECONDS"' `HOUR_MINUTE' Hours and minutes `"HOURS:MINUTES"' `DAY_HOUR' Days and hours `"DAYS HOURS"' `YEAR_MONTH' Years and months `"YEARS-MONTHS"' `HOUR_SECOND' Hours, minutes, seconds `"HOURS:MINUTES:SECONDS"' `DAY_MINUTE' Days, hours, minutes `"DAYS HOURS:MINUTES"' `DAY_SECOND' Days, hours, minutes, `"DAYS seconds HOURS:MINUTES:SECONDS"' *MySQL* allows any non-numeric delimiter in the format. The ones shown in the table are the suggested delimiters. If the date is a `DATE' value and your calculations involve only `YEAR', `MONTH' and `DAY' (that is, no time parts), the result is a `DATE' value. Otherwise the result is a `DATETIME' value. mysql> select DATE_ADD("1997-12-31 23:59:59",INTERVAL 1 SECOND); -> 1998-01-01 00:00:00 mysql> select DATE_ADD("1997-12-31 23:59:59",INTERVAL "1:1" MINUTE_SECOND); -> 1998-01-01 00:01:00 mysql> select DATE_SUB("1998-01-01 00:00:00",INTERVAL "1 1:1:1" DAY_SECOND); -> 1997-12-30 22:58:59 mysql> select DATE_ADD("1997-12-31 23:59:59",INTERVAL 1 DAY); -> 1998-01-01 23:59:59 mysql> select DATE_ADD("1998-01-01 00:00:00",INTERVAL "-1 10" DAY_HOUR); -> 1997-12-30 14:00:00 mysql> select DATE_SUB("1998-01-02",INTERVAL 31 DAY); -> 1997-12-02 If you specify an interval value that is too short (does not include all the interval parts that would be expected from the interval type keyword), *MySQL* assumes you have left out the leftmost parts of the interval value. For example, if you specify a `type' of `DAY_SECOND', the value of `expr' is expected to have day, hours, minutes and seconds parts. If you specify a value like `"1:10"', *MySQL* assumes that the day and hours parts are missing and the the value represents minutes and seconds. In other words, `"1:10" DAY_SECOND' is interpreted as `"1:10" MINUTE_SECOND'. If you use incorrect dates, the result is `NULL'. If you add `MONTH', `YEAR_MONTH' or `YEAR' and the resulting date has a day that is larger than the maximum day for the new month, the day is adjusted to the maximum days in the new month. mysql> select date_add('1998-01-30',Interval 1 month); -> 1998-02-28 `TO_DAYS(date)' Given a date `date', returns a daynumber (the number of days since year 0). `TO_DAYS()' is not intended for use with values that precede the advent of the Gregorian calendar (1582). mysql> select TO_DAYS(950501); -> 728779 mysql> select TO_DAYS('1997-10-07); -> 729669 `FROM_DAYS(N)' Given a daynumber `N', returns a `DATE' value. `FROM_DAYS()' is not intended for use with values that precede the advent of the Gregorian calendar (1582). mysql> select FROM_DAYS(729669); -> '1997-10-07' `DATE_FORMAT(date,format)' Formats the `date' value according to the `format' string. The following specifiers may be used in the `format' string: `%M' Month name (`January'..`December') `%W' Weekday name (`Sunday'..`Saturday') `%D' Day of the month with english suffix (`1st', `2nd', `3rd', etc.) `%Y' Year, numeric, 4 digits `%y' Year, numeric, 2 digits `%a' Abbreviated weekday name (`Sun'..`Sat') `%d' Day of the month, numeric (`00'..`31') `%e' Day of the month, numeric (`0'..`31') `%m' Month, numeric (`01'..`12') `%c' Month, numeric (`1'..`12') `%b' Abbreviated month name (`Jan'..`Dec') `%j' Day of year (`001'..`366') `%H' Hour (`00'..`23') `%k' Hour (`0'..`23') `%h' Hour (`01'..`12') `%I' Hour (`01'..`12') `%l' Hour (`1'..`12') `%i' Minutes, numeric (`00'..`59') `%r' Time, 12-hour (`hh:mm:ss [AP]M') `%T' Time, 24-hour (`hh:mm:ss') `%S' Seconds (`00'..`59') `%s' Seconds (`00'..`59') `%p' `AM' or `PM' `%w' Day of the week (`0'=Sunday..`6'=Saturday) `%U' Week (`0'..`52'), where Sunday is the first day of the week. `%u' Week (`0'..`52'), where Monday is the first day of the week. `%%' Single `%' characters are ignored. Use `%%' to produce a literal `%' (for future extensions). All other characters are just copied to the result. mysql> select DATE_FORMAT('1997-10-04 22:23:00', '%W %M %Y'); -> 'Saturday October 1997' mysql> select DATE_FORMAT('1997-10-04 22:23:00', '%H:%i:%s'); -> '22:23:00' mysql> select DATE_FORMAT('1997-10-04 22:23:00', '%D %y %a %d %m %b %j'); -> '4th 97 Sat 04 10 Oct 277' mysql> select DATE_FORMAT('1997-10-04 22:23:00', '%H %k %I %r %T %S %w'); -> '22 22 10 10:23:00 PM 22:23:00 00 6' For the moment, `%' is optional. In future versions of *MySQL*, `%' will be required. `TIME_FORMAT(time,format)' This is used like the `DATE_FORMAT()' function above, but the `format' string may contain only those format specifiers that handle hours, minutes and seconds. Other specifiers produce a `NULL' value or `0'. `CURDATE()' `CURRENT_DATE' Returns today's date. The format is `YYYYMMDD' or `'YYYY-MM-DD'', depending on whether the function is used in a numeric or string context. mysql> select CURDATE(); -> '1997-12-15' mysql> select CURDATE()+0; -> 19971215 `CURTIME()' `CURRENT_TIME' Returns the current time. The format is `HHMMSS' or `'HH:MM:SS'', depending on whether the function is used in a numeric or string context. mysql> select CURTIME(); -> '23:50:26' mysql> select CURTIME()+0; -> 235026 `NOW()' `SYSDATE()' `CURRENT_TIMESTAMP' Returns the current time, in the format `YYYYMMDDHHMMSS' or `'YYYY-MM-DD HH:MM:SS'', depending on whether the function is used in a numeric or string context. mysql> select NOW(); -> '1997-12-15 23:50:26' mysql> select NOW()+0; -> 19971215235026 `UNIX_TIMESTAMP()' `UNIX_TIMESTAMP(date)' If called with no argument, returns a Unix timestamp (seconds in GMT since `'1970-01-01 00:00:00''). Normally, it is called with a `TIMESTAMP'-valued argument, in which case it returns the value of the argument in seconds. `date' may be a `DATE' string, a `DATETIME' string, a `TIMESTAMP', or a number in the format `YYMMDD' or `YYYYMMDD' in local time. mysql> select UNIX_TIMESTAMP(); -> 882226357 mysql> select UNIX_TIMESTAMP('1997-10-04 22:23:00'); -> 875996580 When `UNIX_TIMESTAMP' is used on a `TIMESTAMP' column, the function will get the value without an implicit `string-to-unix-timestamp' conversion. `FROM_UNIXTIME(Unix_timestamp)' Returns a representation of the timestamp value. The format is `YYYYMMDDHHMMSS' or `'YYYY-MM-DD HH:MM:SS'', depending on whether the function is used in a numeric or string context. mysql> select FROM_UNIXTIME(875996580); -> '1997-10-04 22:23:00' mysql> select FROM_UNIXTIME(875996580)+0; -> 19971004222300 `FROM_UNIXTIME(Unix_timestamp,format)' Returns a string representation of the Unix timestamp, formatted according to the `format' string. `format' may contain the same specifiers as those listed in the entry for the `DATE_FORMAT()' function. mysql> select FROM_UNIXTIME(UNIX_TIMESTAMP(), '%Y %D %M %h:%i:%s %x'); -> '1997 23rd December 03:43:30 x' `SEC_TO_TIME(seconds)' Returns the `seconds' argument, converted to hours, minutes and seconds in the format `HHMMSS' or `HH:MM:SS', depending on whether the function is used in a numeric or string context. mysql> select SEC_TO_TIME(2378); -> '00:39:38' mysql> select SEC_TO_TIME(2378)+0; -> 3938 `TIME_TO_SEC(time)' Returns the `time' argument, converted to seconds. mysql> select TIME_TO_SEC('22:23:00'); -> 80580 mysql> select TIME_TO_SEC('00:39:38'); -> 2378 Miscellaneous functions ----------------------- `DATABASE()' Returns the current database name. mysql> select DATABASE(); -> 'test' `USER()' `SYSTEM_USER()' `SESSION_USER()' Returns the current *MySQL* user name. mysql> select USER(); -> 'davida@localhost' `PASSWORD(str)' Calculates a password string from the plaintext password `str'. To store a password in the `user' grant table, this function must be used. mysql> select PASSWORD('badpwd'); -> '7f84554057dd964b' `PASSWORD()' performs password encryption, but it does not do so in the same way that Unix passwords are encrypted. You should not assume that if your Unix password and your *MySQL* password are the same, `PASSWORD()' will result in the same encrypted value as is stored in the Unix password file. See `ENCRYPT()'. `ENCRYPT(str[,salt])' Encrypt `str' using the Unix `crypt()' system call. The `salt' argument should be a string with 2 characters. If `crypt()' is not available on your system, `ENCRYPT()' always returns `NULL'. mysql> select ENCRYPT("hello"); -> 'VxuFAJXVARROc' `LAST_INSERT_ID([expr])' Returns the last automatically-generated value that was set in an `AUTO_INCREMENT' column. *Note `mysql_insert_id()': mysql_insert_id. mysql> select LAST_INSERT_ID(); -> 1 The last ID that was generated is maintained in the server on a per-connection basis. It will not be changed by another client. It will not even be changed if you update another `AUTO_INCREMENT' column with a non-magic value (that is, a value that is not `NULL' and not 0). If `expr' is given in an `UPDATE' clause, then the used value is returned as a last_insert_id value. This can be used to simulate sequences: First create the table: create table sequence (id int not null); insert into sequence values (0); This can now be used to generate sequence numbers with: UPDATE sequence SET id=last_insert_id(id+1); The new id can be read as you would read any normal auto_increment value in *MySQL* (For example `LAST_INSERT_ID()' will return the new id). `FORMAT(X,D)' Formats the number `X' to a format like `'#,###,###.##'' with `D' decimals. mysql> select FORMAT(12332.33, 2); -> '12,332.33' `VERSION()' Returns a string indicating the *MySQL* server version. mysql> select VERSION(); -> '3.21.16-beta-log' `GET_LOCK(str,timeout)' Tries to obtain a lock with a name given by the string `str', with a timeout of `timeout' seconds. Returns `1' if the lock was obtained successfully, `0' if the attempt timed out, or `NULL' if an error occurred (such as running out of memory or the thread was killed with `mysqladmin kill'). A lock is released when you execute `RELEASE_LOCK()', execute a new `GET_LOCK()' or the thread terminates. This function can be used to implement application locks or to simulate record locks. mysql> select GET_LOCK("automatically released",10); -> 1 mysql> select GET_LOCK("test",10); -> 1 mysql> select RELEASE_LOCK("test"); -> 1 mysql> select RELEASE_LOCK("automatically released"); -> NULL `RELEASE_LOCK(str)' Releases the lock named by the string `str' that was obtained with `GET_LOCK()'. Returns `1' if the lock was released, `0' if the lock wasn't locked by this thread and `NULL' if the named lock didn't exist. Functions for use with `GROUP BY' clauses ----------------------------------------- `COUNT(expr)' Returns a count of the number of non-`NULL' rows. mysql> select COUNT(if(length(name)>3,1,NULL)) from student; `COUNT(*)' is optimized to return very quickly if the `SELECT' retrieves from one table, no other columns are retrieved and there is no `WHERE' clause. mysql> select COUNT(*) from student; `AVG(expr)' Returns the average value of `expr'. `MIN(expr)' `MAX(expr)' Returns the minimum or maximum value of `expr'. `MIN()' and `MAX()' may take a string argument; in such cases they return the minimum or maximum string value. `SUM(expr)' Returns the sum of `expr'. `STD(expr)' `STDDEV(expr)' Returns the standard deviation of `expr'. This is an extension to ANSI SQL. The `STDDEV()' form of this function is provided for Oracle compatability. `BIT_OR(expr)' Returns the bitwise `OR' of all bits in `expr'. The calculation is performed with 64-bit precision. `BIT_AND(expr)' Returns the bitwise `AND' of all bits in `expr'. The calculation is performed with 64-bit precision. *MySQL* has extended the use of `GROUP BY'. You can use columns or calculations in the `SELECT' expressions which don't appear in the `GROUP BY' part. This stands for *any possible value for this group*. You can use this to get better performance by avoiding sorting and grouping on unnecessary items. For example, you don't need to group on `b.name' in the following query: mysql> select a.id,b.name,count(*) from a,b where a.id=b.id GROUP BY a.id; In ANSI SQL, you would have to add `customer.name' to the `GROUP BY' for the following query. In *MySQL*, the name is redundant. mysql> select order.custid,customer.name,max(payments) from order,customer where order.custid = customer.custid GROUP BY order.custid; Don't use this feature if the columns you omit from the `GROUP BY' part aren't unique in the group! In some specific cases, you can use `LEAST()' and `GREATEST()' to get a specific column even if it isn't unique. The following gives the value from the row with the smallest "sort" value. substr(LEAST(concat(sort,space(6-length(sort)),column),7,length(column))) Note that you can't yet use expressions in `GROUP BY' or `ORDER BY' clauses. On the other hand, you can use an alias on an expression to solve the problem: mysql> select id,floor(value/100) as val from tbl_name GROUP BY id,val ORDER BY val; `CREATE DATABASE' syntax ======================== CREATE DATABASE db_name `CREATE DATABASE' creates a database with the given name. Rules for allowable database names are given in *Note Legal names::. Databases in *MySQL* are implemented as directories containing files that correspond to tables in the database. Since there are no tables in a database when it is initially created, the `CREATE DATABASE' statement only creates a directory under the *MySQL* data directory. You can also create databases with `mysqladmin'. *Note Programs::. `DROP DATABASE' syntax ====================== DROP DATABASE [IF EXISTS] db_name `DROP DATABASE' drops all tables in the database and deletes the database. *You must be VERY careful with this command!* `DROP DATABASE' returns the number of files that were removed from the database directory. Normally, this is three times the number of tables, since each table corresponds to a `.ISD' file, a `.ISM' file and a `.frm' file. In *MySQL* 3.22 or later, you can use the keywords `IF EXISTS' to prevent an error from occurring if the database doesn't exist. You can also drop databases with `mysqladmin'. *Note Programs::. `CREATE TABLE' syntax ===================== CREATE TABLE tbl_name (create_definition,...) create_definition: col_name type [NOT NULL | NULL] [DEFAULT default_value] [AUTO_INCREMENT] [PRIMARY KEY] [reference_definition] or PRIMARY KEY (index_col_name,...) or KEY [index_name] KEY(index_col_name,...) or INDEX [index_name] (index_col_name,...) or UNIQUE [index_name] (index_col_name,...) or [CONSTRAINT symbol] FOREIGN KEY index_name (index_col_name,...) [reference_definition] or CHECK (expr) type: TINYINT[(length)] [UNSIGNED] [ZEROFILL] or SMALLINT[(length)] [UNSIGNED] [ZEROFILL] or MEDIUMINT[(length)] [UNSIGNED] [ZEROFILL] or INT[(length)] [UNSIGNED] [ZEROFILL] or INTEGER[(length)] [UNSIGNED] [ZEROFILL] or BIGINT[(length)] [UNSIGNED] [ZEROFILL] or REAL[(length,decimals)] [UNSIGNED] [ZEROFILL] or DOUBLE[(length,decimals)] [UNSIGNED] [ZEROFILL] or FLOAT[(length,decimals)] [UNSIGNED] [ZEROFILL] or DECIMAL(length,decimals) [UNSIGNED] [ZEROFILL] or NUMERIC(length,decimals) [UNSIGNED] [ZEROFILL] or CHAR(length) [BINARY] or VARCHAR(length) [BINARY] or DATE or TIME or TIMESTAMP or DATETIME or TINYBLOB or BLOB or MEDIUMBLOB or LONGBLOB or TINYTEXT or TEXT or MEDIUMTEXT or LONGTEXT or ENUM(value1,value2,value3...) or SET(value1,value2,value3...) index_col_name: col_name [(length)] reference_definition: REFERENCES tbl_name [(index_col_name,...)] [MATCH FULL | MATCH PARTIAL] [ON DELETE reference_option] [ON UPDATE reference_option] reference_option: RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT `CREATE TABLE' creates a table with the given name in the current database. Rules for allowable table names are given in *Note Legal names::. Each table is represented by three files in the database directory: *File* *Purpose* `tbl_name.frm' Table definition (form) file `tbl_name.ISD' Data file `tbl_name.ISM' Index file In *MySQL* 3.22, the table name can be given as `db_name.tbl_name'. For more information on the properties of the various column types, see *Note Column types::. * If neither `NULL' nor `NOT NULL' is specified, the column is treated as though `NULL' had been specified. * An integer column may have the additional attribute `AUTO_INCREMENT'. When you insert a value of `NULL' (recommended) or `0' into an `AUTO_INCREMENT' column, the column is set to `value+1', where `value' is the largest value for the column currently in the table. *Note `mysql_insert_id()': mysql_insert_id. If you delete the row containing the maximum value for an `AUTO_INCREMENT' column, the value will be reused. If you delete all rows in the table, the sequence starts over. *Note:* there can be only one `AUTO_INCREMENT' column per table, and it must be indexed. To make *MySQL* compatible with some `ODBC' applications, you can find the last inserted row with the following query: SELECT * FROM tbl_name WHERE auto IS NULL * `NULL' values are handled differently for `TIMESTAMP' columns than for other column types. You cannot store a literal `NULL' in a `TIMESTAMP' column; setting it to `NULL' sets it to the current time. Because `TIMESTAMP' columns behave this way, the `NULL' and `NOT NULL' attributes do not apply in the normal way and are ignored if you specify them. On the other hand, to make it easier for *MySQL* clients to use `TIMESTAMP' columns, the server reports that the `TIMESTAMP' may take `NULL' values, even though `TIMESTAMP' never will actually hold a `NULL' value. You can see this when you use `DESCRIBE tbl_name' to get a description of your table. Note that setting a `TIMESTAMP' column to `0' is not the same as setting it to `NULL', because `0' is a valid `TIMESTAMP' value. * If no `DEFAULT' value is specified for a column, and the column is *not* declared as `NOT NULL', the default value is `NULL'. * If no `DEFAULT' value is specified for a column, and the column is declared as `NOT NULL', *MySQL* automatically assigns a default value for the field. The default depends on the column type: - For numeric types, the default is `0'. Exception: for an `AUTO_INCREMENT' column, the default value is the next value in the sequence. - For date and time types, the default is the appropriate "zero" value for the type. Exception: if the field is the first `TIMESTAMP' column in the table, the default value is the current time. *Note Date and time types::. - For string types, the default is the empty string. * `KEY' is a synonym for `INDEX'. * In *MySQL*, a `UNIQUE' key can have only distinct values. An error occurs if you try to add a new row with a key that matches an existing row. * A `PRIMARY KEY' is a unique `KEY'. A table can have only one `PRIMARY KEY'. *MySQL* marks the first `UNIQUE' key as the `PRIMARY KEY' if no `PRIMARY KEY' is specified explicitly. * A `PRIMARY KEY' can be a multiple-column index. However, you cannot create a multiple-column index using the `PRIMARY KEY' key attibute in a column specification; doing so will mark only that single column as primary. You must use the `PRIMARY KEY(index_col_name...)' syntax. * If you don't assign a name to an index, the index will be assigned the same name as the first `index_col_name' with an optional suffix (`_2', `_3', ...) to make it unique. You can see index names for a table using `SHOW INDEX FROM tbl_name'. *Note Show::. * Columns that are indexed or part of an index cannot have `NULL' values. You must declare such columns `NOT NULL' or an error results. * With `col_name(length)' syntax, you can specify an index which uses only a part of a `CHAR' or `VARCHAR' column. This can make the index file much smaller. *Note Indexes::. * `TEXT' and `BLOB' columns cannot be indexed. * When you sort or group on a `TEXT' or `BLOB' column, only the first `max_sort_length' bytes are used. *Note `BLOB' limitations: BLOB limitations. * The `FOREIGN KEY', `CHECK' and `REFERENCES' clauses don't actually do anything. The syntax for them is provided only for compatibility, to make it easier to port code from other SQL servers and to run applications that create tables with references. *Note Missing functions::. * Each `NULL' column takes one bit extra, rounded up to the nearest byte. * The maximum record length can be calculated as follows: row length = 1 + (sum of column lengths) + (number of NULL columns + 7)/8 + (number of variable-length columns) Silent column specification changes ----------------------------------- In some cases, *MySQL* silently changes a column specification from that given in the `CREATE TABLE' statement: * `VARCHAR' columns with a length less than four are changed to `CHAR'. * If any column in a table has a variable length, the entire row is variable-length as a result. Therefore, if a table contains any variable-length columns (`VARCHAR', `TEXT' or `BLOB'), all `CHAR' columns longer than three characters are changed to `VARCHAR's. This doesn't affect how you use the columns in any way; in *MySQL*, `VARCHAR' is just a different way to store characters. *MySQL* does the conversion because it saves space and makes table operations faster. *Note Row format::. * `TIMESTAMP' display sizes must be even and in the range from 2 to 14. If you specify a display size of 0 or greater than 14, the size is coerced to 14. Odd-valued sizes in the range from 1 to 13 are coerced to the next higher even number. Certain other column type changes may occur if you compress a table using `pack_isam'. *Note Row format::. `ALTER TABLE' syntax ==================== ALTER [IGNORE] TABLE tbl_name alter_spec [, alter_spec ...] alter_specification: ADD [COLUMN] create_definition [FIRST | AFTER column_name ] or ADD INDEX [index_name] (index_col_name,...) or ADD UNIQUE [index_name] (index_col_name,...) or ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT} or CHANGE [COLUMN] old_col_name create_definition or DROP [COLUMN] col_name or DROP PRIMARY KEY or DROP INDEX key_name or RENAME [AS] new_tbl_name `ALTER TABLE' allows you to change the structure of any existing table. For example, you can add or delete columns, create or destroy indexes, change the type of existing columns, or rename columns or the table itself. `ALTER TABLE' works by making a temporary copy of the original table. The alteration is performed on the copy, then the original table is deleted and the new one is renamed. This is done in such a way that all updates are automatically redirected to the new table without any failed updates. While `ALTER TABLE' is executing, the original table is readable by other clients. Updates and writes to the table are stalled until the new table is ready. * To use `ALTER TABLE', you need *select*, *insert*, *delete*, *update*, *create* and *drop* privileges on the table. * You can issue multiple `ADD', `ALTER', `DROP' and `CHANGE' clauses in a single `ALTER TABLE' statement. This is a *MySQL* extension to ANSI SQL92, which allows only one of each clause per `ALTER TABLE' statement. * `IGNORE' is a *MySQL* extension to ANSI SQL92. It controls how `ALTER TABLE' works if there are duplicates on unique keys in the new table. If `IGNORE' isn't specified, the copy is aborted and rolled back. If `IGNORE' is specified, then for rows with duplicates on a unique key, only the first row is used; the others are deleted. * `CHANGE col_name', `DROP col_name' and `DROP INDEX' are *MySQL* extensions to ANSI SQL92. * The optional word `COLUMN' is a pure noise word and can be omitted. * If you use `ALTER TABLE tbl_name RENAME AS new_name' without any other options, *MySQL* simply renames the files that correspond to the table `tbl_name'. There is no need to create the temporary table. * `create_definition' uses the same syntax for `ADD' and `CHANGE' as for `CREATE TABLE'. *Note Create table::. * You can rename a column using a `CHANGE old_col_name create_definition' clause. To do so, specify the old and new column names and the type that the column currently has. For example, to rename an `INTEGER' column from `a' to `b', you can do this: mysql> ALTER TABLE t1 CHANGE a b INTEGER; If you want to change a column's type, but not the name, the syntax still requires two column names even if they are the same. For example: mysql> ALTER TABLE t1 CHANGE b b BIGINT NOT NULL; * In *MySQL* 3.22 or later, you can use `FIRST' or `ADD ... AFTER col_name' to add a column at a specific position within a table row. The default is to add the column last (at the end of the row). * `ALTER COLUMN' specifies a new default value for a column or removes the old default value. If the old default is removed and the column can be `NULL', the new default is `NULL'. If the column cannot be `NULL', *MySQL* assigns a default value. Default value assignment is described in *Note Create table::. * `DROP INDEX' removes an index. This is a *MySQL* extension to ANSI SQL92. * If columns are dropped from a table, the columns are also removed from any index of which they are a part. If all columns that make up an index are dropped, the index is dropped as well. * `DROP PRIMARY KEY' drops the primary index. If no such index exists, it drops the first `UNIQUE' index in the table. (*MySQL* marks the first `UNIQUE' key as the `PRIMARY KEY' if no `PRIMARY KEY' was specified explicitly.) * When you change a column type using `CHANGE', *MySQL* tries to convert data to the new type as well as possible. * With the C API function `mysql_info()', you can find out how many records were copied, and (when `IGNORE' is used) how many records were deleted due to duplication of unique key values. * The `FOREIGN KEY', `CHECK' and `REFERENCES' clauses don't actually do anything. The syntax for them is provided only for compatibility, to make it easier to port code from other SQL servers and to run applications that create tables with references. *Note Missing functions::. Here is an example that shows some of the uses of uses of `ALTER TABLE'. We begin with a table `t1' that is created as shown below: mysql> CREATE TABLE t1 (a INTEGER,b CHAR(10)); To rename the table from `t1' to `t2': mysql> ALTER TABLE t1 RENAME t2; To change column `a' from `INTEGER' to `TINYINT NOT NULL' (leaving the name the same), and change column `b' from `CHAR(10)' to `CHAR(20)' (and rename it from `b' to `c'): mysql> ALTER TABLE t2 CHANGE a a TINYINT NOT NULL, CHANGE b c CHAR(20); To add a new `TIMESTAMP' column named `d': mysql> ALTER TABLE t2 ADD d TIMESTAMP; To add an index on column `d', and make column `a' the primary key: mysql> ALTER TABLE t2 ADD INDEX (d), ADD PRIMARY KEY (a); To remove column `c': mysql> ALTER TABLE t2 DROP COLUMN c; To add a new `AUTO_INCREMENT' integer column named `c' which cannot be `NULL', and index it at the same time (since `AUTO_INCREMENT' columns must be indexed): mysql> ALTER TABLE t2 ADD c INT UNSIGNED NOT NULL AUTO_INCREMENT, ADD INDEX (c); `OPTIMIZE TABLE' syntax ======================= OPTIMIZE TABLE tbl_name `OPTIMZE TABLE' should be used if you have deleted a large part of the table or if you have made many changes to a table with variable-length rows (tables that have `VARCHAR', `BLOB' or `TEXT' columns). Deleted records are maintained in a linked list and subsequent `INSERT' operations reuse old record positions. You can use `OPTIMIZE TABLE' to reclaim the unused space. `OPTIMIZE TABLE' works by making a temporary copy of the original table. The old table is copied to the new table (without the unused rows), then the original table is deleted and the new one is renamed. This is done in such a way that all updates are automatically redirected to the new table without any failed updates. While `OPTIMIZE TABLE' is executing, the original table is readable by other clients. Updates and writes to the table are stalled until the new table is ready. `DROP TABLE' syntax =================== DROP TABLE [IF EXISTS] tbl_name [, tbl_name...] `DROP TABLE' removes one or more tables. All table data and the table definition are *removed*, so take it easy with this command! In *MySQL* 3.22 or later, you can use the keywords `IF EXISTS' to prevent an error from occurring for tables that don't exist. `DELETE' syntax =============== DELETE [LOW_PRIORITY] FROM tbl_name [WHERE where_definition] `DELETE' deletes rows from `tbl_name' that satisfy the condition given by `where_definition', and returns the number of records affected. If you issue a `DELETE' with no `WHERE' clause, all rows are deleted. *MySQL* does this by recreating the table as an empty table, which is much faster than deleting each row. In this case, `DELETE' returns zero as the number of affected records. (*MySQL* can't return the number of rows that were actually deleted, since the recreate is done without opening the data files. As long as the table definition file `tbl_name.frm' is valid, the table can be recreated this way, even if the data or index files have become corrupted.) If you specify the keyword `LOW_PRIORITY', execution of the `DELETE' is delayed until no other clients are reading from the table. Deleted records are maintained in a linked list and subsequent `INSERT' operations reuse old record positions. To get smaller files, use the `OPTIMIZE TABLE' statement or the `isamchk' utility to reorganize tables. `OPTIMIZE TABLE' is easier, but `isamchk' is faster. *Note Optimization::. `SELECT' syntax =============== SELECT [STRAIGHT_JOIN] [SQL_SMALL_RESULT] [DISTINCT | ALL] select_expression,... [INTO OUTFILE 'file_name' export_options] [FROM table_references [WHERE where_definition] [GROUP BY col_name,...] [HAVING where_definition] [ORDER BY {unsigned_integer | col_name} [ASC | DESC] ,...] [LIMIT [offset,] rows] [PROCEDURE procedure_name] ] `SELECT' is usually used to retrieve rows selected from one or more tables. `SELECT' may also be used to retrieve rows computed without reference to any table. For example: mysql> SELECT 1 + 1; -> 2 All keywords used must be given in exactly the order shown above. For example, a `HAVING' clause must come after any `GROUP BY' clause and before any `ORDER BY' clause. * A table reference may be aliased using `tbl_name AS alias_name' or `tbl_name alias_name'. * You can refer to a column as `col_name', `tbl_name.col_name' or `db_name.tbl_name.col_name'. You need not specify a `tbl_name' or `db_name.tbl_name' prefix for a column reference in a `SELECT' statement unless the reference would be ambiguous. See *Note Legal names::, for examples of ambiguity that require the more explicit column reference forms. * A `SELECT' expression may be given an alias using `AS'. The alias is used as the expression's column name and can be used with `SORT BY', `ORDER BY' or `HAVING' clauses. For example: mysql> select concat(last_name,' ',first_name) AS full_name from mytable ORDER BY full_name; * The `FROM table_references' clause indicates a list of tables to join (i.e., one or more tables from which to select rows). This list may also contain `LEFT OUTER JOIN' references. *Note Join::. * In `LIKE' expressions, the wildcard characters `%' and `_' may be preceded with `\' to suppress their usual wildcard meaning and search for literal instances of `%' and `_'. * Columns selected for output may be referred to in `ORDER BY' and `GROUP BY' clauses using column names, column aliases or column numbers. Column numbers begin with 1. * The `HAVING' clause can refer to any column or alias named in the `select_expression'. It is applied last, just before items are sent to the client, with no optimization. Don't use `HAVING' for items that should be in the `WHERE' clause. For example, do not write this: mysql> select col_name from tbl_name HAVING col_name > 0; Write this instead: mysql> select col_name from tbl_name WHERE col_name > 0; In *MySQL* 3.22.5 or later, you can also write queries like this: mysql> select user,max(salary) from users group by user HAVING max(salary)>10; In older *MySQL* versions, you can write this instead: mysql> select user,max(salary) AS sum from users group by user HAVING sum>10; * `STRAIGHT_JOIN' forces the optimizer to join the tables in the same order as that in which the tables are listed in the `FROM' clause. You can use this to speed up a query if the optimizer joins the tables in non-optimal order. *Note Explain::. * `SQL_SMALL_RESULT' can be used with `GROUP BY' or `DISTINCT' to tell the optimizer that it the result set will be small. In this case *MySQL* will use fast temporary tables to store the resulting table instead of using sorting. * `LIMIT' takes one or two numeric arguments: - If one argument is given, it indicates the maximum number of rows to return. mysql> select * from table LIMIT 5; # Retrieve first 5 rows - If two arguments are given, the first specifies the offset of the first row to return, the second specifies the maximum number of rows to return. The offset of the initial row is 0 (not 1). mysql> select * from table LIMIT 5,10; # Retrieve rows 5-14 * The `SELECT ... INTO OUTFILE 'file_name'' form of `SELECT' writes the selected rows to a file. The file is created on the server host, and cannot already exist (among other things, this prevents database tables and files such as `/etc/passwd' from being destroyed). `SELECT ... INTO OUTFILE' is the complement of `LOAD DATA INFILE'; the syntax for the `export_options' part of the statement consists of the same `FIELDS' and `LINES' clauses that are used with the `LOAD DATA INFILE' statement. *Note Load::. Note that, by default, the escape character, `ASCII 0' (nul) and all terminator characters will be escaped when you use `INTO OUTFILE'. `JOIN' syntax ============= *MySQL* supports the following `JOIN' syntaxes for use in `SELECT' statements: table_reference, table_reference table_reference [CROSS] JOIN table_reference table_reference STRAIGHT_JOIN table_reference table_reference LEFT [OUTER] JOIN table_reference ON conditional_expr table_reference LEFT [OUTER] JOIN table_reference USING (column_list) table_reference NATURAL LEFT [OUTER] JOIN table_reference { oj table_reference LEFT OUTER JOIN table_reference ON conditional_expr } The last `LEFT OUTER JOIN' syntax shown above exists only for compatibility with ODBC. * A table reference may be aliased using `tbl_name AS alias_name' or `tbl_name alias_name'. * `JOIN' and `,' (comma) are semantically identical. Both do a full join between the tables used. Normally, you specify how the tables should be linked in the `WHERE' condition. * The `ON' conditional is any conditional of the form that may be used in a `WHERE' clause. If there is no matching record for the right table in a `LEFT JOIN', a row with all columns set to `NULL' is used for the right table. You can use this fact to find records in a table that have no counterpart in another table: mysql> select table1.* from table1 LEFT JOIN table2 ON table1.id=table2.id where table2.id is NULL; This example finds all rows in `table1' with an `id' value that is not present in `table2' (i.e., all rows in `table1' with no corresponding row in `table2'). This assumes that `table2.id' is declared `NOT NULL', of course. * The `USING' `column_list' clause names a list of columns that must exist in both tables. A `USING' clause such as: A LEFT JOIN B USING (C1,C2,C3...) is defined to be semantically identical to an `ON' expression like this: A.C1=B.C1 AND A.C2=B.C2 AND A.C3=B.C3... * The `NATURAL LEFT JOIN' of two tables is defined to be semantically identical to a `USING' with all column names that exist in both tables. * `STRAIGHT_JOIN' is identical to `JOIN', except that the left table is always read before the right table. This can be used in the few cases where the join optimizer puts the tables in the wrong order. Some examples: mysql> select * from table1,table2 where table1.id=table2.id; mysql> select * from table1 LEFT JOIN table2 ON table1.id=table2.id; mysql> select * from table1 LEFT JOIN table2 USING (id); mysql> select * from table1 LEFT JOIN table2 ON table1.id=table2.id LEFT JOIN table3 ON table3.id=table2.id; `INSERT' syntax =============== INSERT [LOW_PRIORITY] [IGNORE] [INTO] tbl_name [(col_name,...)] VALUES (expression,...),(...),... or INSERT [LOW_PRIORITY] [INTO] tbl_name [(col_name,...)] SELECT ... or INSERT [LOW_PRIORITY] [INTO] tbl_name SET col_name=expression, col_name=expression,... `INSERT' inserts new rows into an existing table. The `INSERT ... VALUES' form inserts rows based on explicitly-specified values. The `INSERT ... SELECT' form inserts rows selected from another table or tables. The `INSERT ... VALUES' form with multiple value lists is supported in *MySQL* 3.22.5 or later. The `col_name=expression' syntax is supported in *MySQL* 3.22.10 and later. `tbl_name' is the table to insert rows into. The column name list indicates which columns the rest of the statement specifies values for. * If you specify no column list, values for all columns must be given. If you don't know the order of the columns in the table, use `DESCRIBE tbl_name' to find out. * If you specify a column list that doesn't name all the columns in the table, columns not named are set to their default values. Default value assignment is described in *Note Create table::. * If *MySQL* was configured using the `DONT_USE_DEFAULT_FIELDS' option, `INSERT' statements generate an error unless you explicitly specify values for all columns that require a non-`NULL' value. *Note `configure' options: configure options. * If you insert `NULL' into a `TIMESTAMP' column, the column is set to the current time. If you insert other values, the column is simply set to the value specified. * An `expression' may refer to any column that was set earlier in a value list. For example, you can say this: mysql> INSERT INTO tbl_name (colA,colB) VALUES(15,colA*2); But not this: mysql> INSERT INTO tbl_name (colA,colB) VALUES(colB*2,15); * If you specify the keyword `LOW_PRIORITY', execution of the `INSERT' is delayed until no other clients are reading from the table. * If you don't specify the keyword `IGNORE' to an `INSERT' with many value rows, the insert will be aborted if there is any row with a similar `PRIMARY' or `UNIQUE' key in the table. If you specify `IGNORE', the rows with a duplicate key value will be not be inserted. You can check with the `mysql_info()' how many rows was inserted into the table. * The following conditions hold for a `INSERT INTO ... SELECT' statement: - The query cannot contain an `ORDER BY' clause. - The target table of the `INSERT' statement cannot appear in the `FROM' clause of the `SELECT' part of the query, because it's forbidden in ANSI SQL to `SELECT' from the same table into which you are `INSERT'ing. (The problem is that the `SELECT' possibly would find records that were inserted earlier during the same run. When using sub-select clauses, the situation could easily be very confusing!) - `AUTO_INCREMENT' columns work as usual. If you use `INSERT INTO ... SELECT ...' or a `INSERT INTO ... VALUES()' statement with multiple value lists, you can use the C API function `mysql_info()' to get information about the query. The format of the information string is shown below: Records: 100 Duplicates: 0 Warnings: 0 `Duplicates' indicates the number of rows which couldn't be inserted because some unique index value in existing rows would be duplicated. `Warnings' indicates the number of attempts to insert column values that were problematic in some way. Warnings can occur under any of the following conditions: * Inserting `NULL' into a column that has been declared `NOT NULL'. The column is set to its default value. * Setting a numeric column to a value that lies outside the column's range. The value is clipped to the appropriate endpoint of the range. * Setting a numeric column to a value such as `10.34 a'. The trailing garbage is stripped and the remaining numeric part is inserted. If the value doesn't make sense as a number at all, the column is set to `0'. * Inserting a string into a `CHAR', `VARCHAR', `TEXT' or `BLOB' column that exceeds the column's maximum length. The value is truncated to the column's maximum length. * Inserting a value into a date or time column that is illegal for the column type. The column is set to the appropriate "zero" value for the type. `REPLACE' syntax ================ REPLACE [LOW_PRIORITY] [INTO] tbl_name [(col_name,...)] VALUES (expression,...) or REPLACE [LOW_PRIORITY] [INTO] tbl_name [(col_name,...)] SELECT ... or REPLACE [LOW_PRIORITY] [INTO] tbl_name SET col_name=expression, col_name=expression,... `REPLACE' works exactly like `INSERT', except that if an old record in the table has the same value on a unique index as a new record, the old record is deleted before the new record is inserted. *Note Insert::. `LOAD DATA INFILE' syntax ========================= LOAD DATA [LOCAL] INFILE 'file_name.txt' [REPLACE | IGNORE] INTO TABLE tbl_name [FIELDS [TERMINATED BY '\t'] [OPTIONALLY] ENCLOSED BY ''] [ESCAPED BY '\\' ]] [LINES TERMINATED BY '\n'] [(col_name,...)] The `LOAD DATA INFILE' statement reads rows from a text file into a table at a very high speed. If the `LOCAL' keyword is specified, the file is read from the client host. If `LOCAL' is not specified, the file must be located on the server. (`LOCAL' is available in *MySQL* 3.22.6 or later.) Using `LOCAL' will be a bit slower than letting the server access the files directly, since the contents of the file must travel from the client host to the server host. The `mysqlimport' utility can be used to read data files; it operates by sending a `LOAD DATA INFILE' command to the server. The `--local' option causes `mysqlimport' to read data files from the client host. You can specify the `--compress' option to get better performance over slow networks if the client and server support the compressed protocol. When locating files on the server host, the server uses the following rules: * If an absolute pathname is given, the server uses the pathname as is. * If a relative pathname with one or more leading components is given, the server searches for the file relative to the server's data directory. * If a filename with no leading components is given, the server looks for the file in the database directory. Note that these rules mean a file given as `myfile.txt' is read from the database directory, whereas a file given as `./myfile.txt' is read from the server's data directory. For security reasons, when reading text files from the server, the files must either reside in the database directory or be readable by all. Also, to use `LOAD DATA INFILE' on server files, you must have the *file* privilege for the database. *Note Privileges::. `LOAD DATA INFILE' is the complement of `SELECT ... INTO OUTFILE'. *Note Select::. To write data from a database to a file, use `SELECT ... INTO OUTFILE'. To read the file back into the database, use `LOAD DATA INFILE'. The syntax of the `FIELDS' and `LINES' clauses is the same for both commands. Both clauses are optional, but `FIELDS' must precede `LINES' if both are specified. If you specify a `FIELDS' clause, each of its subclauses (`TERMINATED BY', `[OPTIONALLY] ENCLOSED BY' and `ESCAPED BY') is also optional, except that you must specify at least one of them. If you don't specify a `FIELDS' clause, the defaults are the same as if you had written this: FIELDS TERMINATED BY '\t' ENCLOSED BY '' ESCAPED BY '\\' If you don't specify a `LINES' clause, the default is the same as if you had written this: LINES TERMINATED BY '\n' In other words, the defaults cause `SELECT ... INTO OUTFILE' to act as follows when writing output: * Write tabs between fields * Do not enclose fields within any quoting characters * Use `\' to escape instances of tab, newline or `\' that occur within field values * Write newlines at the ends of lines Conversely, the defaults cause `LOAD DATA INFILE' to act as follows when reading input: * Look for line boundaries at newlines * Break lines into fields at tabs * Do not expect fields to be enclosed within any quoting characters * Interpret occurrences of tab, newline or `\' preceded by `\' as literal characters that are part of field values Note that to write `FIELDS ESCAPED BY '\\'', you must specify two backslashes for the value to be read as a single backslash. When you use `SELECT ... INTO OUTFILE' in tandem with `LOAD DATA INFILE' to write data from a database into a file and then read the file back into the database later, the field and line handling options for both commands must match. Otherwise, `LOAD DATA INFILE' will not interpret the contents of the file properly. Suppose you use `SELECT ... INTO OUTFILE' to write a file with fields delimited by commas: mysql> SELECT * FROM table1 INTO OUTFILE 'data.txt' FIELDS TERMINATED BY ',' FROM ... To read the comma-delimited file back in, the correct statement would be: mysql> LOAD DATA INFILE 'data.txt' INTO TABLE table2 FIELDS TERMINATED BY ','; If instead you tried to read in the file with the statement shown below, it wouldn't work because it instructs `LOAD DATA INFILE' to look for tabs between fields: mysql> LOAD DATA INFILE 'data.txt' INTO TABLE table2 FIELDS TERMINATED BY '\t'; The likely result is that each input line would be interpreted as a single field. `LOAD DATA INFILE' can be used to read files obtained from external sources, too. For example, a file in DBASE format will have fields separated by commas and enclosed in double quotes. If lines in the file are terminated by newlines, the command shown below illustrates the field and line handling options you would use to load the file: mysql> LOAD DATA INFILE 'file_name.txt' INTO TABLE tbl_name FIELDS TERMINATED BY ',' ENCLOSED BY '"' LINES TERMINATED BY '\n'; Any of the field or line handling options may specify an empty string (`'''). If not empty, the `FIELDS [OPTIONALLY] ENCLOSED BY' and `FIELDS ESCAPED BY' values must be a single character. The `FIELDS TERMINATED BY' and `LINES TERMINATED BY' values may be more than one character. For example, to write lines that are terminated by carriage return-linefeed pairs, or to read a file containing such lines, specify a `LINES TERMINATED BY '\r\n'' clause. `FIELDS [OPTIONALLY] ENCLOSED BY' controls quoting of fields. For output (`SELECT ... INTO OUTFILE'), if you omit the word `OPTIONALLY', all fields are enclosed by the `ENCLOSED BY' character. An example of such output (using a comma as the field delimiter) is shown below: "1","a string","100.20" "2","a string containing a , comma","102.20" "3","a string containing a \" quote","102.20" "4","a string containing a \", quote and comma","102.20" If you specify `OPTIONALLY', the `ENCLOSED BY' character is used only to enclose `CHAR' and `VARCHAR' fields: 1,"a string",100.20 2,"a string containing a , comma",102.20 3,"a string containing a \" quote",102.20 4,"a string containing a \", quote and comma",102.20 Note that occurrences of the `ENCLOSED BY' character within a field value are escaped by prefixing them with the `ESCAPED BY' character. Also note that if you specify an empty `ESCAPED BY' value, you may generate output that cannot be read properly by `LOAD DATA INFILE'. For example, the output just shown above would appear as shown below if the escape character is empty. Observe that the second field in the fourth line contains a comma following the quote, which (erroneously) appears to terminate the field: 1,"a string",100.20 2,"a string containing a , comma",102.20 3,"a string containing a " quote",102.20 4,"a string containing a ", quote and comma",102.20 For input, the `ENCLOSED BY' character, if present, is stripped from the ends of field values. (This is true whether or not `OPTIONALLY' is specified; `OPTIONALLY' has no effect on input interpretation.) Occurrences of the `ENCLOSED BY' character preceded by the `ESCAPED BY' character are interpreted as part of the current field value. In addition, duplicated `ENCLOSED BY' characters occurring within fields are interpreted as single `ENCLOSED BY' characters if the field itself starts with that character. For example, if `ENCLOSED BY '"'' is specified, quotes are handled as shown below: "The ""BIG"" boss" -> The "BIG" boss The "BIG" boss -> The "BIG" boss The ""BIG"" boss -> The ""BIG"" boss `FIELDS ESCAPED BY' controls how to write or read special characters. If the `FIELDS ESCAPED BY' character is not empty, it is used to prefix the following characters on output: * The `FIELDS ESCAPED BY' character * The `FIELDS [OPTIONALLY] ENCLOSED BY' character * The first character of the `FIELDS TERMINATED BY' and `LINES TERMINATED BY' values * ASCII 0 (what is actually written following the escape character is ASCII `'0'', not a zero-valued byte) If the `FIELDS ESCAPED BY' character is empty, no characters are escaped. It is probably not a good idea to specify an empty escape character, particularly if field values in your data contain any of the characters in the list just given. For input, if the `FIELDS ESCAPED BY' character is not empty, occurrences of that character are stripped and the following character is taken literally as part of a field value. The exceptions are an escaped `0' or `N' (e.g., `\0' or `\N' if the escape character is `\'). These sequences are interpreted as ASCII 0 (a zero-valued byte) and `NULL'. See below for the rules on `NULL' handling. For more information about `\'-escape syntax, see *Note Base Syntax::. In certain cases, field and line handling options interact: * If `LINES TERMINATED BY' is an empty string and `FIELDS TERMINATED BY' is non-empty, lines are also terminated with `FIELDS TERMINATED BY'. * If the `FIELDS TERMINATED BY' and `FIELDS ENCLOSED BY' values are both empty (`'''), a fixed-row (non-delimited) format is used. With fixed-row format, no delimiters are used between fields. Instead, column values are written and read using the "display" widths of the columns. For example, if a column is declared as `INT(7)', values for the column are written using 7-character fields. On input, values for the column are obtained by reading 7 characters. Fixed-row format also affects handling of `NULL' values; see below. Handling of `NULL' values varies, depending on the `FIELDS' and `LINES' options you use: * For the default `FIELDS' and `LINES' values, `NULL' is written as `\N' for output and `\N' is read as `NULL' for input (assuming the `ESCAPED BY' character is `\'). * If `FIELDS ENCLOSED BY' is not empty, a field value of the literal word `NULL' is read as a `NULL' value (this differs from the word `NULL' enclosed within `FIELDS ENCLOSED BY' characters, which is read as the string `'NULL''). * If `FIELDS ESCAPED BY' is empty, `NULL' is written as the word `NULL'. * With fixed-row format (which happens when `FIELDS TERMINATED BY' and `FIELDS ENCLOSED BY' are both empty), `NULL' is written as a blank string. Note that this makes `NULL' values and blank values indistinguishable in the file. If you need to be able to tell the two apart when reading the file back in, you should not use fixed-row format. The `REPLACE' and `IGNORE' keywords control handling of input records that duplicate existing records on unique key values. If you specify `REPLACE', new rows replace existing rows that have the same unique key value. If you specify `IGNORE', input rows that duplicate an existing row on a unique key value are skipped. If you don't specify either option, an error occurs when a duplicate key value is found, and the rest of the text file is ignored. Some cases are not supported by `LOAD DATA INFILE': * Fixed-size rows (`FIELDS TERMINATED BY' and `FIELDS ENCLOSED BY' both empty) and `BLOB' columns. * If you specify one separator that is the same as or a prefix of another, `LOAD DATA INFILE' won't be able to interpret the input properly. For example, the following `FIELDS' clause would cause problems: FIELDS TERMINATED BY '"' ENCLOSED BY '"' * If `FIELDS ESCAPED BY' is empty, a field value that contains an occurrence of `FIELDS ENCLOSED BY' or `LINES TERMINATED BY' followed by the `FIELDS TERMINATED BY' value will cause `LOAD DATA INFILE' to stop reading a field or line too early. This happens because `LOAD DATA INFILE' cannot properly determine where the field or line value ends. The following example loads all columns of the `persondata' table: mysql> LOAD DATA INFILE 'persondata.txt' INTO TABLE persondata; No field list is specified, so `LOAD DATA INFILE' expects input rows to contain a field for each table column. The default `FIELDS' and `LINES' values are used. If you wish to load only some of a table's columns, specify a field list: mysql> LOAD DATA INFILE 'persondata.txt' INTO TABLE persondata (col1,col2,...); You must also specify a field list if the order of the fields in the input file differs from the order of the columns in the table, so that *MySQL* can tell how to match up input fields with table columns. If a row has too few fields, the columns for which no input field is present are set to default values. `TIMESTAMP' columns are only set to the current time if there is a `NULL' value for the column, or (for the first `TIMESTAMP' column only) if the `TIMESTAMP' column is left out from the field list when a field list is specified. Default value assignment is described in *Note Create table::. If an input row has too many fields, the extra fields are ignored and a warning is generated. `LOAD DATA INFILE' regards all input as strings, so you can't use numeric values for `ENUM' or `SET' columns the way you can with `INSERT' statements. All `ENUM' and `SET' values must be given as strings! When the `LOAD DATA INFILE' query finishes, you can use the C API function `mysql_info()' to get information about the query. The format of the information string is shown below: Records: 1 Deleted: 0 Skipped: 0 Warnings: 0 Warnings occur under the same circumstances as when values are inserted via the `INSERT' statement (*note Insert::.), except that `LOAD DATA INFILE' also generates warnings when there are too few or too many fields in the input row. For more information about the efficiency of `INSERT' versus `LOAD DATA INFILE' and speeding up `LOAD DATA INFILE', see *Note Table efficiency::. `UPDATE' syntax =============== UPDATE [LOW_PRIORITY] tbl_name SET col_name1=expr1,col_name2=expr2,... [WHERE where_definition] `UPDATE' updates columns in existing table rows with new values. The `WHERE' clause, if given, specifies which rows should be updated. Otherwise all rows are updated. If you specify the keyword `LOW_PRIORITY', execution of the `UPDATE' is delayed until no other clients are reading from the table. If you access a `tbl_name' column in an expression, `UPDATE' uses the current value of the column. For example, the following statement sets the `age' column to one more than its current value: mysql> UPDATE persondata SET age=age+1; `UPDATE' assignments are evaluated from left to right. For example, the following statement doubles the `age' column, then increments it: mysql> UPDATE persondata SET age=age*2,age=age+1; If you set a column to the value it currently has, *MySQL* notices this and doesn't update it. `UPDATE' returns the number of rows that were actually changed. In *MySQL* 3.22 or later, the C API function `mysql_info()' returns the number of rows that were matched and updated and the number of warnings that occurred during the `UPDATE'. `USE' syntax ============ USE db_name The `USE db_name' statement tells *MySQL* to use the `db_name' database as the default database for subsequent queries. The database remains current until the end of the session, or until another `USE' statement is issued: mysql> USE db1; mysql> SELECT count(*) FROM mytable; ; selects from db1.mytable mysql> USE db2; mysql> SELECT count(*) FROM mytable; ; selects from db2.mytable Making a particular database current by means of the `USE' statement does not preclude you from accessing tables in other databases. The example below accesses the `author' table from the `db1' database and the `editor' table from the `db2' database: mysql> USE db1; mysql> SELECT author_name,editor_name FROM author,db2.editor WHERE author.editor_id = db2.editor.editor_id; The `USE' statement is provided for Sybase compatibility. `FLUSH' syntax (clearing caches) ================================ FLUSH flush_option [,flush_option] You should use the `FLUSH' command if you want to clear some of the internal caches *MySQL* uses. `flush_option' can be any of the following: `HOSTS' Empties the host cache tables. You should flush the host tables if some of your hosts change IP number or if you get the error message `Host ... is blocked'. (When too many connections errors occur for a given host, *MySQL* assumes something is wrong and blocks the host from further connection requests. Flushing the host tables allows the host to attempt to connect again. *Note Blocked host::.) `LOGS' Closes and reopens the standard and update log files. If you have specified the update log file without an extension, the extension number of the new update log file will be incremented by 1 relative to the previous file. `PRIVILEGES' Reloads the privileges from the grant tables in the `mysql' database. `TABLES' Closes all open tables. `STATUS' Reset most status variables to zero. You can also access each of the commands shown above with the `mysqladmin' utility, using the `flush-hosts', `flush-logs', `reload' or `flush-tables' commands. To execute the `FLUSH' command, you must have the *reload* privilege. `KILL' syntax ============= KILL thread_id Each connection to `mysqld' runs in a separate thread. You can see which threads are running with the `SHOW PROCESSLIST' command, and kill a thread with the `KILL thread_id' command. If you do not have the *process* privilege, you can see and kill only your own threads. You can also use `mysqladmin processlist' and `mysqladmin kill' to examine and kill threads. `SHOW' syntax (Get information about tables, columns...) ======================================================== SHOW DATABASES [LIKE wild] or SHOW TABLES [FROM db_name] [LIKE wild] or SHOW COLUMNS FROM tbl_name [FROM db_name] [LIKE wild] or SHOW INDEX FROM tbl_name [FROM db_name] or SHOW STATUS or SHOW VARIABLES [LIKE wild] or SHOW PROCESSLIST `SHOW' provides information about databases, tables, columns or the server. If the `LIKE wild' part is used, the `wild' string should be a normal SQL wildcard string that uses the `%' and `_' wildcard characters. Instead of using `tbl_name FROM db_name' syntax, you can also use `db_name.tbl_name'. These two statements are equivalent: mysql> SHOW INDEX FROM mytable FROM mydb; mysql> SHOW INDEX FROM mydb.mytable; `SHOW DATABASES' lists the databases on the *MySQL* server host. You can also get this list using the `mysqlshow' command. `SHOW TABLES' lists the tables in a given database. You can also get this list using the `mysqlshow db_name' command. *NOTE*: If a user doesn't have any privileges for a table, the table will not show up when requesting a list of tables with `SHOW TABLES' or `mysqlshow db_name'. `SHOW FIELDS' is a synonym for `SHOW COLUMNS' and `SHOW KEYS' is a synonym for `SHOW INDEX'. You can also list a table's columns or indexes with `mysqlshow db_name tbl_name' or `mysqlshow -k db_name tbl_name'. `SHOW STATUS' provides server status information (like `mysqladmin extended-status'). The output resembles that shown below, though the format and numbers may differ somewhat: +------------------------+-------+ | Variable_name | Value | +------------------------+-------+ | Created_tmp_tables | 0 | | Deletes | 0 | | Flush_tables | 1 | | Key_blocks_used | 2 | | Key_read_requests | 4 | | Key_reads | 2 | | Key_write_requests | 0 | | Key_writes | 0 | | Not_flushed_key_blocks | 0 | | Open_tables | 1 | | Open_files | 2 | | Open_streams | 0 | | Opened_tables | 12 | | Questions | 25 | | Read_key | 2 | | Read_next | 2 | | Read_rnd | 35 | | Read_first | 0 | | Running_threads | 1 | | Slow_queries | 0 | | Uptime | 36944 | | Write | 0 | +------------------------+-------+ `SHOW VARIABLES' shows the values of the some of *MySQL* system variables. You can also get this information using the `mysqladmin variables' command. If the default values are unsuitable, you can set most of these variables using command-line options when `mysqld' starts up. `SHOW PROCESSLIST' shows you which threads are running. You can also get this information using the `mysqladmin processlist' command. If you do not have the *process* privilege, you can see only your own threads. *Note Kill::. `EXPLAIN' syntax (Get information about a `SELECT') =================================================== EXPLAIN SELECT select_options When you precede a `SELECT' statement with the keyword `EXPLAIN', *MySQL* explains how it would process the `SELECT', providing information about how tables are joined and in which order. With the help of `EXPLAIN', you can see when you must add indexes to tables to get a faster `SELECT' that uses indexes to find the records. You can also see if the optimizer joins the tables in an optimal order. To force the optimizer to use a specific join order for a `SELECT' statement, add a `STRAIGHT_JOIN' clause. For non-simple joins, `EXPLAIN' returns a row of information for each table used in the `SELECT' statement. The tables are listed in the order they would be read. *MySQL* resolves all joins using a one-sweep multi-join method. This means that *MySQL* reads a row from the first table, then finds a matching row in the second table, then in the third table and so on. When all tables are processed, it outputs the selected columns and the table list is back-tracked until a table is found for which there are more matching rows. The next row is read from this table and the process continues with the next table. Output from `EXPLAIN' includes the following columns: `table' The table to which the row of output refers. `type' The join type. Information about the various types is given below. `possible_keys' The `possible_keys' column indicates which indexes *MySQL* could use to find the rows in the table. If this column is empty, there are no relevant indexes. In this case, you may be able to improve the performance of your query by examining the `WHERE' clause to see if it refers to some column or columns that would be suitable for indexing. If so, create an appropriate index and check the query with `EXPLAIN' again. To see what indexes a table has, use `SHOW INDEX FROM tbl_name'. `key' The `key' column indicates the key that *MySQL* actually decided to use. The key is `NULL' if no index was chosen. `key_len' The `key_len' column indicates the length of the key that *MySQL* decided to use. The length is `NULL' if the `key' is `NULL'. `ref' The `ref' column shows which columns or constants are used with the `key' to select rows from the table. `rows' The `rows' column indicates the number of rows *MySQL* must examine to execute the query. `Extra' If the `Extra' column includes the text `Only index', this means that only information from the index tree is used to retrieve information from the table (which should be much faster than scanning the entire table). If the `Extra' column includes the text `where used', it means that a `WHERE' clause will be used to restrict which rows will be matched against the next table or sent to the client. The different join types are listed below, ordered from best to worst type: `system' The table has only one row (= system table). This is a special case of the `const' join type. `const' The table has at most one matching row, which will be read at the start of the query. Since there is only one row, values from the column in this row can be regarded as constants by the rest of the optimizer. `const' tables are very fast as they are read only once! `eq_ref' One row will be read from this table for each combination of rows from the previous tables. This the best possible join type, other than the `const' types. It is used when all parts of an index are used by the join and the index is `UNIQUE' or a `PRIMARY KEY'. `ref' All rows with matching index values will be read from this table for each combination of rows from the previous tables. `ref' is used if the join uses only a leftmost prefix of the key, or if the key is not `UNIQUE' or a `PRIMARY KEY' (in other words, if the join cannot select a single row based on the key value). If the key that is used matches only a few rows, this join type is good. `range' Only rows that are in a given range will be retrieved, using an index to select the rows. The `ref' column indicates which index is used. `index' This is the same as `ALL', except that only the index tree is scanned. This is usually faster than `ALL', as the index file is usually smaller than the data file. `ALL' A full table scan will be done for each combination of rows from the previous tables. This is normally not good if the table is the first table not marked `const', and usually *very* bad in all other cases. You normally can avoid `ALL' by adding more indexes, so that the row can be retrieved based on constant values or column values from earlier tables. You can get a good indication of how good a join is by multiplying all values in the `rows' column of the `EXPLAIN' output. This should tell you roughly how many rows *MySQL* must examine to execute the query. This number is also used when you restrict queries with the `max_join_size' variable. *Note MySQL parameters:: The following example shows how a `JOIN' can be optimized progressively using the information provided by `EXPLAIN'. Suppose you have the `SELECT' statement shown below, that you examine using `EXPLAIN': EXPLAIN SELECT tt.TicketNumber, tt.TimeIn, tt.ProjectReference, tt.EstimatedShipDate, tt.ActualShipDate, tt.ClientID, tt.ServiceCodes, tt.RepetitiveID, tt.CurrentProcess, tt.CurrentDPPerson, tt.RecordVolume, tt.DPPrinted, et.COUNTRY, et_1.COUNTRY, do.CUSTNAME FROM tt, et, et AS et_1, do WHERE tt.SubmitTime IS NULL AND tt.ActualPC = et.EMPLOYID AND tt.AssignedPC = et_1.EMPLOYID AND tt.ClientID = do.CUSTNMBR; For this example, assume that: * The columns being compared have been declared as follows: *Table* *Column* *Column type* `tt' `ActualPC' `CHAR(10)' `tt' `AssignedPC' `CHAR(10)' `tt' `ClientID' `CHAR(10)' `et' `EMPLOYID' `CHAR(15)' `do' `CUSTNMBR' `CHAR(15)' * The tables have the indexes shown below: *Table* *Index* `tt' `ActualPC' `tt' `AssignedPC' `tt' `ClientID' `et' `EMPLOYID' (primary key) `do' `CUSTNMBR' (primary key) * The `tt.ActualPC' values aren't evenly distributed. Initially, before any optimizations have been performed, the `EXPLAIN' statement produces the following information: table type possible_keys key key_len ref rows Extra et ALL PRIMARY NULL NULL NULL 74 do ALL PRIMARY NULL NULL NULL 2135 et_1 ALL PRIMARY NULL NULL NULL 74 tt ALL AssignedPC,ClientID,ActualPC NULL NULL NULL 3872 range checked for each record (key map: 35) This output indicates that *MySQL* is doing a full join for all tables--`type' is `ALL' for each table! This will take quite a long time, as the product of the number of rows in each table must be examined! For the case at hand, this is `74 * 2135 * 74 * 3872 = 45,268,558,720' rows. If the tables were bigger, you can only imagine how long it would take... One problem here is that *MySQL* can't (yet) use indexes on columns efficiently if they are declared differently. `VARCHAR' and `CHAR' are not different in this context, unless they are not declared to be the same length. Since `tt.ActualPC' is declared as `CHAR(10)' and `et.EMPLOYID' is declared as `CHAR(15)', there is a length mismatch. To fix this disparity between column lengths, use `ALTER TABLE' to lengthen `ActualPC' from 10 characters to 15 characters: mysql> ALTER TABLE tt CHANGE ActualPC ActualPC VARCHAR(15); Now `tt.ActualPC' and `et.EMPLOYID' are both `VARCHAR(15)'. Executing the `EXPLAIN' statement again produces this result: table type possible_keys key key_len ref rows Extra tt ALL AssignedPC,ClientID,ActualPC NULL NULL NULL 3872 where used do ALL PRIMARY NULL NULL NULL 2135 range checked for each record (key map: 1) et_1 ALL PRIMARY NULL NULL NULL 74 range checked for each record (key map: 1) et eq_ref PRIMARY PRIMARY 15 tt.ActualPC 1 This is not perfect, but is much better (the product of the `rows' values is now less by a factor of 74). This version is executed in a couple of seconds. A second alteration can be made to eliminate the column length mismatches in the `tt.AssignedPC = et_1.EMPLOYID' and `tt.ClientID = do.CUSTNMBR' comparisons: mysql> ALTER TABLE tt CHANGE AssignedPC AssignedPC VARCHAR(15), CHANGE ClientID ClientID VARCHAR(15); Now `EXPLAIN' produces the output shown below: table type possible_keys key key_len ref rows Extra et ALL PRIMARY NULL NULL NULL 74 tt ref AssignedPC,ClientID,ActualPC ActualPC 15 et.EMPLOYID 52 where used et_1 eq_ref PRIMARY PRIMARY 15 tt.AssignedPC 1 do eq_ref PRIMARY PRIMARY 15 tt.ClientID 1 This is "almost" as good as it can get. The remaining problem is that, by default, *MySQL* assumes that values in the `tt.ActualPC' column are evenly distributed, and that isn't the case for the `tt' table. Fortunately, it is easy to tell *MySQL* about this: shell> isamchk --analyze PATH_TO_MYSQL_DATABASE/tt shell> mysqladmin refresh Now the join is "perfect", and `EXPLAIN' produces this result: table type possible_keys key key_len ref rows Extra tt ALL AssignedPC,ClientID,ActualPC NULL NULL NULL 3872 where used et eq_ref PRIMARY PRIMARY 15 tt.ActualPC 1 et_1 eq_ref PRIMARY PRIMARY 15 tt.AssignedPC 1 do eq_ref PRIMARY PRIMARY 15 tt.ClientID 1 `DESCRIBE' syntax (Get information about columns) ================================================= {DESCRIBE | DESC} tbl_name {col_name | wild} `DESCRIBE' provides information about a table's columns. `col_name' may be a column name or a string containing the SQL `%' and `_' wildcard characters. This statement is provided for Oracle compatibility. The `SHOW' statement provides similar information. *Note Show::. `LOCK TABLES/UNLOCK TABLES' syntax ================================== LOCK TABLES tbl_name [AS alias] {READ | [LOW_PRIORITY] WRITE} [, tbl_name {READ | [LOW_PRIORITY] WRITE} ...] ... UNLOCK TABLES `LOCK TABLES' locks tables for the current thread. `UNLOCK TABLES' releases any locks held by the current thread. All tables that are locked by the current thread are automatically unlocked when the thread issues another `LOCK TABLES', or when the connection to the server is closed. If a thread obtains a `READ' lock on a table, that thread (and all other threads) can only read from the table. If a thread obtains a `WRITE' lock on a table, then only the thread holding the lock can `READ' from or `WRITE' to the table. Other threads are blocked. Each thread waits (without timing out) until it obtains all the locks it has requested. `WRITE' locks normally have higher priority than `READ' locks, to ensure that updates are processed as soon as possible. This means that if one thread obtains a `READ' lock and then another thread requests a `WRITE' lock, subsequent `READ' lock requests will wait until the `WRITE' thread has gotten the lock and released it. You can use `LOW_PRIORITY WRITE' locks to allow other threads to obtain `READ' locks while the thread is waiting for the `WRITE' lock. You should only use `LOW_PRIORITY WRITE' locks if you are sure that there will eventually be time when there are no threads that have a `READ' lock. When you use `LOCK TABLES', you must lock all tables that you are going to use! If you are using a table multiple times in a query (with alias), you have to get a lock for each alias! This policy ensures that table locking is deadlock free. Normally, you don't have to lock tables, as all single `UPDATE' statements are atomic; no other thread can interfere with any other currently executing SQL statement. There are a few cases when you would like to lock tables anyway: * If you are going to run many operations on a bunch of tables, it's much faster to lock the tables you are going to use. The downside is, of course, that no other thread can update a `READ'-locked table and no other thread can read a `WRITE'-locked table. * As *MySQL* doesn't support a transaction environment, you must use `LOCK TABLES' if you want to ensure that no other thread comes between a `SELECT' and an `UPDATE'. For example, the example shown below requires `LOCK TABLES' in order to execute safely! Without `LOCK TABLES', there is a chance that another thread might insert a new row in the `trans' table between execution of the `SELECT' and `UPDATE' statements: mysql> LOCK TABLES trans READ, customer WRITE; mysql> SELECT SUM(value) FROM trans WHERE customer_id= some_id; mysql> UPDATE customer SET total_value=sum_from_previous_statement WHERE customer_id=some_id; mysql> UNLOCK TABLES; By using incremental updates (`UPDATE customer set value=value+new_value') or the `LAST_INSERT_ID()' function you can avoid using `LOCK TABLES' in many cases. You can also solve some cases by using the user-level lock functions `GET_LOCK()' and `RELEASE_LOCK()'. These locks are saved in a hash table in the server and implemented with `pthread_mutex_lock()' and `pthread_mutex_unlock()' for high speed. *Note Miscellaneous functions::. See *Note Internal locking::, for more information on locking policy. `SET OPTION' syntax =================== SET [OPTION] SQL_VALUE_OPTION= value, ... `SET OPTION' sets various options that affect the operation of the server or your client. Any option you set remains in effect until the current session ends, or until you set the option to a different value. The options are: `CHARACTER SET character_set_name | DEFAULT' This maps all strings from and to the client with the given mapping. Currently the only option for `character_set_name' is `cp1251_koi8', but you can easily add new mappings by editing the `sql/convert.cc' file in the *MySQL* source distribution. The default mapping can be restored by using a `character_set_name' value of `DEFAULT'. Note that the syntax for setting the `CHARACTER SET' option differs from the syntax for setting the other options. `PASSWORD = PASSWORD('some password')' Set the password for the current user. Any non-anonymous user can change his password! `PASSWORD FOR user = PASSWORD('some password')' Set the password for a specific user on the current host. Only a user with database access to the `mysql' database can do this. The user should be given in `user@hostname' format, where `user' and `hostname' are exactly as they are listed in the `User' and `Host' columns of the `mysql.user' table entry. For example, if you had an entry with `User' and `Host' fields of `'bob'' and `'%.loc.gov'', you would write: mysql> SET PASSWORD FOR bob@"%.loc.gov" = PASSWORD("newpass"); `SQL_BIG_TABLES= 0 | 1' If set to 1, all temporary tables are stored on disk rather than in memory. This will be a little slower, but you will not get the error `The table tbl_name is full' for big `SELECT' operations that require a large temporary table. The default value for a new connection is `0' (i.e., use in-memory temporary tables). `SQL_BIG_SELECTS= 0 | 1' If set to `1', *MySQL* will abort if a `SELECT' is attempted that probably will take a very long time. This is useful when an inadvisable `WHERE' statement has been issued. A big query is defined as a `SELECT' that probably will have to examine more than `max_join_size' rows. The default value for a new connection is `0' (which will allow all `SELECT' statements). `SQL_LOW_PRIORITY_UPDATES= 0 | 1' If set to `1', all `INSERT', `UPDATE' and `DELETE' statements wait until there is no pending `SELECT' on the affected table. `SQL_SELECT_LIMIT= value | DEFAULT' The maximum number of records to return from `SELECT' statements. If a `SELECT' has a `LIMIT' clause, the `LIMIT' takes precedence over the value of `SQL_SELECT_LIMIT'. The default value for a new connection is "unlimited". If you have changed the limit, the default value can be restored by using a `SQL_SELECT_LIMIT' value of `DEFAULT'. `SQL_LOG_OFF= 0 | 1' If set to `1', no logging will be done to the standard log for this client, if the client has the *process* privilege. This does not affect the update log! `SQL_UPDATE_LOG= 0 | 1' If set to `0', no logging will be done to the update log for the client, if the client has the *process* privilege. This does not affect the standard log! `TIMESTAMP= timestamp_value | DEFAULT' Set the time for this client. This is used to get the original timestamp if you use the update log to restore rows. `LAST_INSERT_ID= #' Set the value to be returned from `LAST_INSERT_ID()'. This is stored in the update log when you use `LAST_INSERT_ID()' in a command that updates a table. `INSERT_ID= #' Set the value to be used by the following `INSERT' command when inserting an `AUTO_INCREMENT' value. This is mainly used with the update log. `GRANT' and `REVOKE' syntax =========================== GRANT priv_type [(column_list)] [, priv_type [(column_list)] ...] ON {tbl_name | * | *.* | db_name.*} TO user_name [IDENTIFIED BY 'password'] [, user_name [IDENTIFIED BY 'password'] ...] [WITH GRANT OPTION] REVOKE priv_type [(column_list)] [, priv_type [(column_list)] ...] ON {tbl_name | * | *.* | db_name.*} FROM user_name [, user_name ...] `GRANT' is implemented in *MySQL* 3.22.11 and up. For earlier *MySQL* versions, the `GRANT' statement does nothing. The purpose of the `GRANT' and `REVOKE' commands is to enable system administrators to grant and revoke rights to *MySQL* users at four privilege levels: *Global level* Global privileges apply to all databases on the server. These privileges are stored in the `mysql.user' table. *Database level* Database privileges apply to all tables in a given database. These privileges are stored in the `mysql.db' and `mysql.host' tables. *Table level* Table privileges apply to all columns in a table. These privileges are stored in the `mysql.tables_priv' table. *Column level* Column privileges apply to single columns in a table. These privileges are stored in the `mysql.columns_priv' table. For examples of how `GRANT' works, see *Note Adding users::. For the `GRANT' and `REVOKE' statements, `priv_type' may be specified as any of the following: ALL PRIVILEGES FILE RELOAD ALTER INDEX SELECT CREATE INSERT SHUTDOWN DELETE PROCESS UPDATE DROP REFERENCES USAGE `ALL' is a synonym for `ALL PRIVILEGES'. `REFERENCES' is not yet implemented. `USAGE' is currently a synonym for "no privileges". It can be used when you want to create a user that has no privileges. To revoke the *grant* privilege from a user, use a `priv_type' value of `GRANT OPTION': REVOKE GRANT OPTION ON ... FROM ...; The only `priv_type' values you can specify for a table are `SELECT', `INSERT', `UPDATE', `DELETE', `CREATE', `DROP', `GRANT', `INDEX' and `ALTER'. The only `priv_type' values you can specify for a column (that is, when you use a `column_list' clause) are `SELECT', `INSERT' and `UPDATE'. You can set database privileges by using `ON db_name.*' syntax. If you specify `ON *' and you have a current database, you will set the privileges for that database. If you specify `ON *' and you don't have a current database, or if you specify `ON *.*', you will affect the global privileges. In order to accommodate granting rights to users from other hosts, *MySQL* supports specifying the `user_name' value in the form `user@host'. If you want to specify a `user_name' value containing wildcard characters or special characters (such as `%'), you can quote the user or host name (e.g., `'test-user'@'test-hostname''). You can specify wildcards in the hostname. For example, `user@"%.loc.gov"' applies to `user' for any host in the `loc.gov' domain, and `user@"144.155.166.%"' applies to `user' for any host in the `144.155.166' class C subnet. The simple form `user' is a synonym for `user@"%"'. *NOTE:* If you allow anonymous users (this is the default) to connect to the *MySQL* server, you should add all local user with username@localhost because else the anonymous user will be used when the user tries to log into the *MySQL* server from the same machine! Anonymous users is defined by inserting entries with user=" into the `mysql.user' table. You can verify if this applies to you by executing: select host,user from mysql.user where user=''; For the moment, `GRANT' only supports host, table, database and column names up to 60 characters long. A user name can be up to 16 characters. The total access rights for a table or column are formed from the logical `OR' of the privileges at each of the four privilege levels. For example, if the `mysql.user' table specifies that a user has a global *select* privilege, this can't be denied by an entry at the database, table or column level. The total rights for a column can be calculated as follows: global rights OR (database rights AND host rights) OR table rights OR column rights In most cases, you grant rights to a user at one of the different privilege levels, so life isn't normally as complicated as above. :) The details of the access-right checking procedure are presented in *Note Privilege system::. If you grant privileges for a user/hostname combination that does not exist in the `mysql.user' table, an entry is added and remains there until deleted with a `DELETE' command. In *MySQL* 3.22.12 and up, if a new user is created or if you have global grant privileges, the user's password will be set to the password specified by the `IDENTIFIED BY' clause, if one is given. If the user already had a password, it is replaced by the new one. Passwords can also be set with the `SET PASSWORD' command. *Note Set option::. If you grant privileges for a database, an entry in the `mysql.db' table is created if needed. When all privileges for the database have been removed with `REVOKE', this entry is deleted. If a user doesn't have any privileges on a table, the table is not displayed when the user requests a list of tables (e.g., with a `SHOW TABLES' statement). The `WITH GRANT OPTION' clause gives the user the ability to give to other users any privileges the user has at the specified privilege level. You should be careful to whom you give the *grant* privilege, as two users with different privileges may be able to join privileges! You cannot grant another user a privilege you don't have yourself; the *grant* privilege allows you to give away only those privileges you possess. Be aware that when you grant a user the *grant* privilege at a particular privilege level, any privileges the user already possesses (or is given in the future!) at that level are also grantable by that user. Suppose you grant a user the *insert* privilege on a database. If you then grant the *select* privilege on the database and specify `WITH GRANT OPTION', the user can give away not only the *select* privilege, but also *insert*. If you then grant the *update* privilege to the user on the database, the user can give away the *insert*, *select* and *update*. You should not grant *alter* privileges to a normal user. If you do that, the user can try to subvert the privilege system by renaming tables! Note that if you are using table/column privileges for even one user, *MySQL* examines table/column privileges for all users and this will slow down `mysqld' a bit. When `mysqld' starts, all privileges are read into memory. Database, table and column privileges take effect at once and user level privileges take effect the next time the user connects. Modifications to the grant tables that you perform using `GRANT' or `REVOKE' are noticed by the server immediately. If you modify the grant tables manually (using `INSERT', `UPDATE', etc.), you should execute a `FLUSH PRIVILEGES' statement or run `mysqladmin flush-privileges' to tell the server to reload the grant tables. *Note Privilege changes::. The biggest differences between the ANSI SQL and *MySQL* versions of `GRANT' are: * ANSI SQL doesn't have global or database level privileges and ANSI SQL doesn't support all privilege types that *MySQL* supports. * When you drop a table in ANSI SQL, all privileges for the table are revoked. If you revoke a privilege in ANSI SQL, all privileges that were granted based on this privilege are also revoked. In *MySQL*, privileges can be dropped only with explicit `REVOKE' commands or by manipulating the *MySQL* grant tables. `CREATE INDEX' syntax (Compatibility function) ============================================== CREATE [UNIQUE] INDEX index_name ON tbl_name (col_name[(length]),... ) The `CREATE INDEX' statement doesn't do anything in *MySQL* prior to version 3.22. In 3.22 or later, `CREATE INDEX' is mapped to an `ALTER TABLE' call to create indexes. *Note Alter table::. Normally, you create all indexes on a table at the time the table itself is created with `CREATE TABLE'. *Note Create table::. `CREATE INDEX' allows you to add indexes to existing tables. A column list of the form `(col1,col2,...)' creates a multiple-column index. Index values are formed by concatenating the values of the given columns. For `CHAR' and `VARCHAR' columns, indexes can be created that use only part of a column, using `col_name(length)' syntax. The statement shown below creates an index using the first 10 characters of the `name' column: mysql> CREATE INDEX part_of_name ON customer (name(10)); Use of partial columns for indexes can make the index file much smaller. Since most names usually differ in the first 10 characters, this index should not be much slower than an index created from the entire `name' column, it could save a lot of disk space and might also speed up `INSERT' operations! For more information about how *MySQL* uses indexes, see *Note *MySQL* indexes: MySQL indexes. `DROP INDEX' syntax (Compatibility function) ============================================ DROP INDEX index_name `DROP INDEX' doesn't do anything in *MySQL* prior to version 3.22. In 3.22 or later, `DROP INDEX' is mapped to an `ALTER TABLE' call to drop the `INDEX' or `UNIQUE' definition. *Note Alter table::. Comment syntax ============== *MySQL* supports the `# to end of line' and `/* in-line or multiple-line */' comment styles: mysql> select 1+1; # This comment continues to the end of line mysql> select 1 /* this is an in-line comment */ + 1; mysql> select 1+ /* this is a multiple-line comment */ 1; *MySQL* doesn't support the `--' ANSI SQL comment style. *Note Missing comments::. `CREATE FUNCTION/DROP FUNCTION' syntax ====================================== CREATE FUNCTION function_name RETURNS {STRING|REAL|INTEGER} SONAME shared_library_name DROP FUNCTION function_name A user-definable function (UDF) is a way to extend *MySQL* with a new function that works like native (built in) *MySQL* functions such as `ABS()' and `CONCAT()'. `CREATE FUNCTION' saves the function's name, type and shared library name in the system table `func' in the `mysql' database. You must have the *insert* and `delete' privileges for the `mysql' database to create and drop functions. All active functions are reloaded each time the server starts, unless you start `mysqld' with the `--skip-grant-tables' option. In this case, UDF initialization is skipped and UDFs are unavailable. (An active function is one that has been loaded with `CREATE FUNCTION' and not removed with `DROP FUNCTION'.) For the UDF mechanism to work, functions must be written in C or C++ and your operating system must support dynamic loading. For information on how to write user-definable functions, see *Note Adding functions::. Is *MySQL* picky about reserved words? ====================================== A common problem stems from trying to create a table with column names like `TIMESTAMP' or `GROUP', the names of datatypes and functions built into *MySQL*. You're allowed to do it (for example, `ABS' is an allowed column name), but whitespace is not allowed between a function name and the `(' when using functions whose names are also column names. The following words are explicitly reserved in *MySQL*. Most of them are forbidden by ANSI SQL92 as column and/or table names (for example, `group'). A few are reserved because *MySQL* needs them and is (currently) using a `yacc' parser: `action' `add' `all' `alter' `after' `and' `as' `asc' `auto_increment' `between' `bigint' `bit' `binary' `blob' `bool' `both' `by' `cascade' `char' `character' `change' `check' `column' `columns' `constraint' `create' `cross' `current_date' `current_time' `current_timestamp'`data' `database' `databases' `date' `datetime' `day' `day_hour' `day_minute' `day_second' `dayofmonth' `dayofweek' `dayofyear' `dec' `decimal' `default' `delete' `desc' `describe' `distinct' `distinctrow' `double' `drop' `escaped' `enclosed' `enum' `explain' `exists' `fields' `first' `float' `float4' `float8' `foreign' `from' `for' `full' `function' `grant' `group' `having' `hour' `hour_minute' `hour_second' `ignore' `in' `index' `infile' `insert' `int' `integer' `interval' `int1' `int2' `int3' `int4' `int8' `into' `if' `is' `join' `key' `keys' `last_insert_id' `leading' `left' `like' `lines' `limit' `load' `lock' `long' `longblob' `longtext' `low_priority' `match' `mediumblob' `mediumtext' `mediumint' `middleint' `minute' `minute_second' `month' `monthname' `natural' `numeric' `no' `not' `null' `on' `option' `optionally' `or' `order' `outer' `outfile' `partial' `password' `precision' `primary' `procedure' `processlist' `privileges' `quarter' `read' `real' `references' `rename' `regexp' `reverse' `repeat' `replace' `restrict' `returns' `rlike' `second' `select' `set' `show' `smallint' `soname' `sql_big_tables' `sql_big_selects' `sql_select_limit' `sql_low_priority_updates'`sql_log_off' `sql_log_update' `straight_join' `starting' `status' `string' `table' `tables' `terminated' `text' `time' `timestamp' `tinyblob' `tinytext' `tinyint' `trailing' `to' `use' `using' `unique' `unlock' `unsigned' `update' `usage' `values' `varchar' `variables' `varying' `varbinary' `with' `write' `where' `year' `year_month' `zerofill' The following symbols (from the table above) are disallowed by ANSI SQL but allowed by *MySQL* as column/table names. This is because some of these names are very natural names and a lot of people have already used them. * `ACTION' * `BIT' * `DATE' * `ENUM' * `NO' * `TEXT' * `TIME' * `TIMESTAMP' Example SQL queries ******************* Queries from twin project ========================= At Analytikerna and Lentus, we have been doing the systems and field work for a big research project. This project is a collaboration between the Institute of Environmental Medicine at Karolinska Institutet Stockholm and the Section on Clinical Research in Aging and Psychology at the University of Southern California. The project involves a screening part where all twins in Sweden older than 65 years are interviewed by telephone. Twins who meet certain criteria are passed on to the next stage. In this latter stage, twins who want to participate are visited by a doctor/nurse team. Some of the examinations include physical and neuropsychological examination, laboratory testing, neuroimaging, psychological status assessment, and family history collection. In addition, data are collected on medical and environmental risk factors. More information about Twin studies can be found at `http://www.imm.ki.se/TWIN/TWINUKW.HTM'. The latter part of the project is administered with a web interface written using Perl and *MySQL*. Each night all data from the interviews are moved into a *MySQL* database. Find all non-distributed twins ------------------------------ The following query is used to determine who goes into the second part of the project: select concat(p1.id, p1.tvab)+0 as tvid, concat(p1.christian_name, " ", p1.surname) as Name, p1.postal_code as Code, p1.city as City, pg.abrev as Area, if(td.participation = "Aborted", "A", " ") as A, p1.dead as dead1, l.event as event1, td.suspect as tsuspect1, id.suspect as isuspect1, td.severe as tsevere1, id.severe as isevere1, p2.dead as dead2, l2.event as event2, h2.nurse as nurse2, h2.doctor as doctor2, td2.suspect as tsuspect2, id2.suspect as isuspect2, td2.severe as tsevere2, id2.severe as isevere2, l.finish_date from twin_project as tp /* For Twin 1 */ left join twin_data as td on tp.id = td.id and tp.tvab = td.tvab left join informant_data as id on tp.id = id.id and tp.tvab = id.tvab left join harmony as h on tp.id = h.id and tp.tvab = h.tvab left join lentus as l on tp.id = l.id and tp.tvab = l.tvab /* For Twin 2 */ left join twin_data as td2 on p2.id = td2.id and p2.tvab = td2.tvab left join informant_data as id2 on p2.id = id2.id and p2.tvab = id2.tvab left join harmony as h2 on p2.id = h2.id and p2.tvab = h2.tvab left join lentus as l2 on p2.id = l2.id and p2.tvab = l2.tvab, person_data as p1, person_data as p2, postal_groups as pg where /* p1 gets main twin and p2 gets his/her twin. */ /* ptvab is a field inverted from tvab */ p1.id = tp.id and p1.tvab = tp.tvab and p2.id = p1.id and p2.ptvab = p1.tvab and /* Just the sceening survey */ tp.survey_no = 5 and /* Skip if partner died before 65 but allow emigration (dead=9) */ (p2.dead = 0 or p2.dead = 9 or (p2.dead = 1 and (p2.death_date = 0 or (((to_days(p2.death_date) - to_days(p2.birthday)) / 365) >= 65)))) and ( /* Twin is suspect */ (td.future_contact = 'Yes' and td.suspect = 2) or /* Twin is suspect - Informant is Blessed */ (td.future_contact = 'Yes' and td.suspect = 1 and id.suspect = 1) or /* No twin - Informant is Blessed */ (ISNULL(td.suspect) and id.suspect = 1 and id.future_contact = 'Yes') or /* Twin broken off - Informant is Blessed */ (td.participation = 'Aborted' and id.suspect = 1 and id.future_contact = 'Yes') or /* Twin broken off - No inform - Have partner */ (td.participation = 'Aborted' and ISNULL(id.suspect) and p2.dead = 0)) and l.event = 'Finished' /* Get at area code */ and substring(p1.postal_code, 1, 2) = pg.code /* Not already distributed */ and (h.nurse is NULL or h.nurse=00 or h.doctor=00) /* Has not refused or been aborted */ and not (h.status = 'Refused' or h.status = 'Aborted' or h.status = 'Died' or h.status = 'Other') order by tvid; Some explanations: `concat(p1.id, p1.tvab)+0 as tvid' We want to sort on the concatenated `id' and `tvab' in numerical order. Adding `0' to the result causes *MySQL* to treat the result as a number. column `id' This identifies a pair of twins. It is a key in all tables. column `tvab' This identifies a twin in a pair. It has a value of `1' or `2'. column `ptvab' This is an inverse of `tvab'. When `tvab' is `1' this is `2', and vice versa. It exists to save typing and to make it easier for *MySQL* to optimize the query. This query demonstrates, among other things, how to do lookups on a table from the same table with a join (`p1' and `p2'). In the example, this is used to check whether a twin's partner died before the age of 65. If so, the row is not returned. All of the above exist in all tables with twin-related information. We have a key on both `id,tvab' (all tables) and `id,ptvab' (`person_data') to make queries faster. On our production machine (A 200MHz UltraSparc), this query returns about 150-200 rows and takes less than one second. The current number of records in the tables used above: *Table* *Rows* `person_data' 71074 `lentus' 5291 `twin_project' 5286 `twin_data' 2012 `informant_data' 663 `harmony' 381 `postal_groups' 100 Show a table on twin pair status -------------------------------- Each interview ends with a status code called `event'. The query shown below is used to display a table over all twin pairs combined by event. This indicates in how many pairs both twins are finished, in how many pairs one twin is finished and the other refused, and so on. select t1.event, t2.event, count(*) from lentus as t1, lentus as t2, twin_project as tp where /* We are looking at one pair at a time */ t1.id = tp.id and t1.tvab=tp.tvab and t1.id = t2.id /* Just the sceening survey */ and tp.survey_no = 5 /* This makes each pair only appear once */ and t1.tvab='1' and t2.tvab='2' group by t1.event, t2.event; *MySQL* Server functions ************************ What languages are supported by *MySQL*? ======================================== `mysqld' can issue error messages in the following languages: Czech, Dutch, English (the default), French, German, Hungarian, Italian, Norwegian, Norwegian-ny, Polish, Portuguese, Spanish and Swedish. To start `mysqld' with a particular language, use either the `--language=lang' or `-L lang' options. For example: shell> mysqld --language=swedish or: shell> mysqld --language=/usr/local/share/swedish Note that all language names are specified in lowercase. The language files are located (by default) in `MYSQL_BASE_DIR/share/LANGUAGE/'. To update the error message file, you should edit the `errmsg.txt' file and execute the following command to generate the `errmsg.sys' file: shell> comp_err errmsg.txt errmsg.sys If you upgrade to a newer version of *MySQL*, remember to repeat your changes with the new `errmsg.txt' file. The character set used for data and sorting ------------------------------------------- By default, *MySQL* uses the ISO-8859-1 (Latin1) character set. This is the character set used in the USA and western Europe. The character set determines what characters are allowed in names and how things are sorted by the `ORDER BY' and `GROUP BY' clauses of the `SELECT' statement. You can change the character set at compile time by using the `--with-charset=charset' option to `configure'. *Note Quick install::. To add another character set to *MySQL*, use the following procedure: Adding a new character set -------------------------- 1. Choose a name for the character set, denoted `MYSET' below. 2. Create the file `strings/ctype-MYSET.c' in the *MySQL* source distribution. 3. Look at one of the existing `ctype-*.c' files to see what needs to be defined. Note that the arrays in your file must have names like `ctype_MYSET', `to_lower_MYSET' and so on. `to_lower[]' and `to_upper[]' are simple arrays that hold the lowercase and uppercase characters corresponding to each member of the character set. For example: to_lower['A'] should contain 'a' to_upper['a'] should contain 'A' `sort_order[]' is a map indicating how characters should be ordered for comparison and sorting purposes. For many character sets, this is the same as `to_upper[]' (which means sorting will be case insensitive). *MySQL* will sort characters based on the value of `sort_order[character]'. `ctype[]' is an array of bit values, with one element for one character. (Note that `to_lower[]', `to_upper[]' and `sort_order[]' are indexed by character value, but `ctype[]' is indexed by character value + 1. This is an old legacy to be able to handle EOF.) You can find the following bitmask definitions in `m_ctype.h': #define _U 01 /* Upper case */ #define _L 02 /* Lower case */ #define _N 04 /* Numeral (digit) */ #define _S 010 /* Spacing character */ #define _P 020 /* Punctuation */ #define _C 040 /* Control character */ #define _B 0100 /* Blank */ #define _X 0200 /* heXadecimal digit */ The `ctype[]' entry for each character should be the union of the applicable bitmask values that describe the character. For example, `'A'' is an uppercase character (`_U') as well as a hexidecimal digit (`_X'), so `ctype['A'+1]' should contain the value: _U + _X = 01 + 0200 = 0201 4. Add a unique number for your character set to `include/m_ctype.h.in'. 5. Add the character set name to the `CHARSETS_AVAILABLE' list in `configure.in'. 6. Reconfigure, recompile and test. Multi-byte character support ---------------------------- If you are creating a multi-byte character set, you can use the `_MB' macros. In `include/m_ctype.h.in', add: #define MY_CHARSET_MYSET X #if MY_CHARSET_CURRENT == MY_CHARSET_MYSET #define USE_MB #define USE_MB_IDENT #define ismbchar(p, end) (...) #define ismbhead(c) (...) #define mbcharlen(c) (...) #define MBMAXLEN N #endif Where: `MY_CHARSET_MYSET' A unique character set value. `USE_MB' This character set has multi-byte characters, handled by `ismbhead()' and `mbcharlen()' `USE_MB_IDENT' (optional) If defined, you can use table and column names that use multi-byte characters `ismbchar(p, e)' return 0 if `p' is not a multi-byte character string, or the size of the character (in bytes) if it is. `p' and `e' point to the beginning and end of the string. Check from `(char*)p' to `(char*)e-1'. `ismbhead(c)' True if `c' is the first character of a multi-byte character string `mbcharlen(c)' Size of a multi-byte character string if `c' is the first character of such a string `MBMAXLEN' Size in bytes of the largest character in the set The update log ============== When started with the `--log-update=file_name' option, `mysqld' writes a log file containing all SQL commands that update data. The file is written in the data directory and has a name of `file_name.#', where `#' is a number that is incremented each time you execute `mysqladmin refresh' or `mysqladmin flush-logs', the `FLUSH LOGS' statement, or restart the server. If you use the `--log' or `-l' options, the filename is `hostname.log', and restarts and refreshes do not cause a new log file to be generated. By default, the `mysql.server' script starts the *MySQL* server with the `-l' option. If you need better performance when you start using *MySQL* in a production environment, you can remove the `-l' option from `mysql.server'. Update logging is smart since it logs only statements that really update data. So an `UPDATE' or a `DELETE' with a `WHERE' that finds no rows is not written to the log. It even skips `UPDATE' statements that set a column to the value it already has. If you want to update a database from update log files, you could do the following (assuming your log files have names of the form `file_name.#'): shell> ls -1 -t -r file_name.[0-9]* | xargs cat | mysql `ls' is used to get all the log files in the right order. This can be useful if you have to revert to backup files after a crash and you want to redo the updates that occurred between the time of the backup and the crash. You can also use the update logs when you have a mirrored database on another host and you want to replicate the changes that have been made to the master database. How big *MySQL* tables can be ============================= *MySQL* itself has a 4G limit on table size, and operating systems have their own file size limits. On Linux, the current limit is 2G; on Solaris 2.5.1, the limit is 4G; on Solaris 2.6, the limit is going to be 1000G. Currently, table sizes are limited to either 4G (the *MySQL* limit) or the operating system limit, whichever is smaller. To get more than 4G requires some changes to *MySQL* that are on the TODO. *Note TODO::. If your big table is going to be read-only, you could use `pack_isam' to merge and compress many tables to one. `pack_isam' usually compresses a table by at least 50%, so you can have, in effect, much bigger tables. *Note `pack_isam': pack_isam. Another solution can be the included MERGE library, which allows you to handle a collection of identical tables as one. (Identical in this case means that all tables are created with identical column information.) Currently MERGE can only be used to scan a collection of tables because it doesn't support indexes. We will add indexes to this in the near future. Getting maximum performance from *MySQL* **************************************** Changing the size of *MySQL* buffers ==================================== You can get the default buffer sizes used by the `mysqld' server with this command: shell> mysqld --help This command produces a list of all `mysqld' options and configurable variables. The output includes the default values and looks something like this: Possible variables for option --set-variable (-O) are: back_log current value: 5 connect_timeout current value: 5 join_buffer current value: 131072 key_buffer current value: 1048540 long_query_time current value: 10 max_allowed_packet current value: 1048576 max_connections current value: 90 max_connect_errors current value: 10 max_join_size current value: 4294967295 max_sort_length current value: 1024 net_buffer_length current value: 16384 record_buffer current value: 131072 sort_buffer current value: 2097116 table_cache current value: 64 tmp_table_size current value: 1048576 thread_stack current value: 131072 wait_timeout current value: 28800 If there is a `mysqld' server currently running, you can see what values it actually is using for the variables by executing this command: shell> mysqladmin variables Each option is described below. Values for buffer sizes, lengths and stack sizes are given in bytes. You can specify values with a suffix of `K' or `M' to indicate kilobytes or megabytes. For example, `16M' indicates 16 megabytes. Case of suffix letters does not matter; `16M' and `16m' are equivalent. ``back_log'' The number of outstanding connection requests *MySQL* can have. This comes into play when the main *MySQL* thread gets *VERY* many connection requests in a very short time. It then takes some time (but very short) for the main thread to check the connection and start a new thread. The `back_log' value indicates how many requests can be stacked during this short time before *MySQL* momentarily stops answering new requests. You need to increase this only if you expect a large number of connections in a short period of time. In other words, this value is the size of the listen queue for incoming TCP/IP connections. Your operating system has its own limit on the size of this queue. The manual page for the Unix system call `listen(2)' should have more details. Check your OS documentation for the maximum value for this variable. Attempting to set `back_log' higher than this maximum will be ineffective. ``connect_timeout'' The number of seconds the `mysqld' server is waiting for a connect packet before responding with `Bad handshake'. ``join_buffer'' The size of the buffer that is used for full joins (joins that do not use indexes). The buffer is allocated one time for each full join between two tables. Increase this value to get a faster full join when adding indexes is not possible. (Normally the best way to get fast joins is to add indexes.) ``key_buffer'' Index blocks are buffered and are shared by all threads. `key_buffer' is the size of the buffer used for index blocks. You might want to increase this value when doing many `DELETE' or `INSERT' operations on a table with lots of indexes. To get even more speed, use `LOCK TABLES'. *Note Lock tables::. ``max_allowed_packet'' The maximum size of one packet. The message buffer is initialized to `net_buffer_length' bytes, but can grow up to `max_allowed_packet' bytes when needed. This value by default is small to catch big (possibly wrong) packets. You must increase this value if you are using big `BLOB' columns. It should be as big as the biggest `BLOB' you want to use. ``max_connections'' The number of simultaneous clients allowed. Increasing this value increases the number of file descriptors that `mysqld' requires. See below for comments on file descriptor limits. ``max_connection_errors'' If there is more than this number of interrupted connections from a host this host will be blocked for further connections. You can unblock a host with the command `FLUSH HOSTS'. ``max_join_size'' Joins that are probably going to read more than `max_join_size' records return an error. Set this value if your users tend to perform joins without a `WHERE' clause that take a long time and return millions of rows. ``max_sort_length'' The number of bytes to use when sorting `BLOB' or `TEXT' values (only the first `max_sort_length' bytes of each value are used; the rest are ignored). ``net_buffer_length'' The communication buffer is reset to this size between queries. This should not normally be changed, but if you have very little memory, you can set it to the expected size of a query. (That is, the expected length of SQL statements sent by clients. If statements exceed this length, the buffer is automatically enlarged, up to `max_allowed_packet' bytes.) ``record_buffer'' Each thread that does a sequential scan allocates a buffer of this size for each table it scans. If you do many sequential scans, you may want to increase this value. ``sort_buffer'' Each thread that needs to do a sort allocates a buffer of this size. Increase this value for faster `ORDER BY' or `GROUP BY' operations. *Note Temporary files::. ``table_cache'' The number of open tables for all threads. Increasing this value increases the number of file descriptors that `mysqld' requires. *MySQL* needs two file descriptors for each unique open table. See below for comments on file descriptor limits. For information about how the table cache works, see *Note Table cache::. ``tmp_table_size'' If a temporary table exceeds this size, *MySQL* generates an error of the form `The table tbl_name is full'. Increase the value of `tmp_table_size' if you do many advanced `GROUP BY' queries. ``thread_stack'' The stack size for each thread. Many of the limits detected by the `crash-me' test are dependent on this value. The default is normally large enough. *Note Benchmarks::. `wait_timeout' The number of seconds the server waits for activity on a connection before closing it. `table_cache' and `max_connections' affect the maximum number of files the server keeps open. If you increase one or both of these values, you may run up against a limit imposed by your operating system on the per-process number of open file descriptors. However, you can increase the limit on many systems. Consult your OS documentation to find out how to do this, because the method for changing the limit varies widely from system to system. `table_cache' is related to `max_connections'. For example, for 200 open connections, you should have a table cache of at least `200 * n', where `n' is the maximum number of tables in a join. *MySQL* uses algorithms that are very scalable, so you can usually run with very little memory or give *MySQL* more memory to get better performance. If you have much memory and many tables and want maximum performance with a moderate number of clients, you should use something like this: shell> safe_mysqld -O key_buffer=16M -O table_cache=128 \ -O sort_buffer=4M -O record_buffer=1M & If you have little memory and lots of connections, use something like this: shell> safe_mysqld -O key_buffer=512k -O sort_buffer=100k \ -O record_buffer=100k & or even: shell> safe_mysqld -O key_buffer=512k -O sort_buffer=16k \ -O table_cache=32 -O record_buffer=8k -O net_buffer=1K & If there are very many connections, "swapping problems" may occur unless `mysqld' has been configured to use very little memory for each connection. `mysqld' performs better if you have enough memory for all connections, of course. Note that if you change an option to `mysqld', it remains in effect only for that instance of the server. To see the effects of a parameter change, do something like this: shell> mysqld -O key_buffer=32m --help Make sure that the `--help' option is last; otherwise, the effect of any options listed after it on the command line will not be reflected in the output. How *MySQL* uses memory ======================= The list below indicates some of the ways that the `mysqld' server uses memory. Where applicable, the name of the server variable relevant to the memory use is given. * The key buffer (variable `key_buffer') is shared by all threads; Other buffers used by the server are allocated as needed. * Each connection uses some thread specific space; A stack (64K, variable `thread_stack') a connection buffer (variable `net_buffer_length'), and a result buffer (variable `net_buffer_length'). The connection buffer and result buffer are dynamicly enlarged up to `max_allowed_packet' when needed. When a query is running a copy of the current query string is also alloced. * All threads share the same base memory. * Nothing is memory-mapped yet (except compressed tables, but that's another story). This is because the 32-bit memory space of 4GB is not large enough for most large tables. When we get a system with a 64-bit address space, we may add general support for memory-mapping. * Each request doing a sequential scan over a table allocates a read buffer (variable `record_buffer'). * All joins are done in one pass and most joins can be done without even using a temporary table. Most temporary tables are memory-based (HEAP) tables. Temporary tables with a big record length (calculated as the sum of all column lengths) or that contain `BLOB' columns are stored on disk. One current problem is that if a HEAP table exceeds the size of `tmp_table_size', you get the error `The table tbl_name is full'. In the future, we will fix this by automatically changing the in-memory (HEAP) table to a disk-based (NISAM) table as necessary. To work around this problem, you can increase the temporary table size by setting the `tmp_table_size' option to `mysqld', or by setting the SQL option `SQL_BIG_TABLES' in the client program. *Note Set option::. In *MySQL* 3.20, the maximum size of the temporary table was `record_buffer*16', so if you are using this version, you have to increase the value of `record_buffer'. You can also start `mysqld' with the `--big-tables' option to always store temporary tables on disk, however, this will affect the speed of all complicated queries. * Most requests doing a sort allocate a sort buffer and one or two temporary files. *Note Temporary files::. * Almost all parsing and calculating is done in a local memory store. No memory overhead is needed for small items and the normal slow memory allocation and freeing is avoided. Memory is allocated only for unexpectedly large strings (this is done with `malloc()' and `free()'). * Each index file is opened once and the data file is opened once for each concurrently-running thread. For each concurrent thread, a table structure, column structures for each column, and a buffer of size `3 * n' is allocated (where `n' is the maximum row length, not counting `BLOB' columns). A `BLOB' uses 5 to 8 bytes plus the length of the `BLOB' data. * For each table having `BLOB' columns, a buffer is enlarged dynamically to read in larger `BLOB' values. If you scan a table, a buffer as large as the largest `BLOB' value is allocated. * Table handlers for all in-use tables are saved in a cache and managed as a FIFO. Normally the cache has 64 entries. If a table has been used by two running threads at the same time, the cache contains two entries for the table. *Note Table cache::. * A `mysqladmin flush-tables' command closes all tables that are not in use and marks all in-use tables to be closed when the currently executing thread finishes. This will effectively free most in-use memory. `ps' and other system status programs may report that `mysqld' uses a lot of memory. This may be caused by thread-stacks on different memory addresses. For example, the Solaris version of `ps' counts the unused memory between stacks as used memory. You can verify this by checking available swap with `swap -s'. We have tested `mysqld' with commercial memory-leakage detectors, so there should be no memory leaks. How compiling and linking affects the speed of *MySQL* ====================================================== Most of the following tests are done on Linux and with the *MySQL* benchmarks, but they should give some indication for other operating systems. You get the fastest executable when you link with `-static'. Using Unix sockets rather than TCP/IP to connect to a database also gives better performance. On Linux, you will get the fastest code when compiling with `pgcc' and `-O6'. To compile `sql_yacc.cc' with these options, you need 180M memory because `gcc/pgcc' needs a lot of memory to make all functions inline. You should also set `CXX=gcc' when configuring *MySQL* to avoid inclusion of the `libstdc++' library. * If you use `pgcc' and compile everything with `-O6', the `mysqld' server is 11% faster than with `gcc'. * If you link dynamically (without `-static'), the result is 13% slower. * If you connect using TCP/IP rather than Unix sockets, the result is 7.5% slower. * On a Sun sparcstation 10, `gcc' 2.7.3 is 13% faster than Sun Pro C++ 4.2. * On Solaris 2.5.1, MIT-pthreads is 8-12% slower than Solaris native threads. The *MySQL*-Linux distribution provided by TcX is compiled with `pgcc' and linked statically. How *MySQL* uses indexes ======================== All indexes (`PRIMARY', `UNIQUE' and `INDEX()') are stored in B-trees. Strings are automatically prefix- and end-space compressed. *Note Create index::. Indexes are used to: * Quickly find the rows that match a `WHERE' clause. * Retrieve rows from other tables when performing joins. * Find the `MAX()' or `MIN()' value for a specific key. * Sort or group a table if the sorting or grouping is done on a leftmost prefix of a usable key (e.g., `ORDER BY key_part_1,key_part_2 '). The key is read in reverse order if all key parts are followed by `DESC'. * Retrieve values without consulting the data file, in some cases. If all used columns for some table are numeric and form a leftmost prefix for some key, the values may be retrieved from the index tree for greater speed. Suppose you issue the following `SELECT' statement: mysql> SELECT * FROM tbl_name WHERE col1=val1 AND col2=val2; If a multiple-column index exists on `col1' and `col2', the appropriate rows can be fetched directly. If separate single-column indexes exist on `col1' and `col2', the optimizer decides which index will find fewer rows and uses that index to fetch the rows. If the table has a multiple-column index, any leftmost prefix of the index can be used by the optimizer to find rows. For example, if you have a three-column index on `(col1,col2,col3)', you have indexed search capabilities on `(col1)', `(col1,col2)' and `(col1,col2,col3)'. *MySQL* can't use a partial index if the columns don't form a leftmost prefix of the index. Suppose you have the `SELECT' statements shown below: mysql> SELECT * FROM tbl_name WHERE col1=val1; mysql> SELECT * FROM tbl_name WHERE col2=val2; mysql> SELECT * FROM tbl_name WHERE col2=val2 AND col3=val3; If an index exists on `(col1,col2,col3)', only the first query shown above uses the index. The second and third queries do involve indexed columns, but `(col2)' and `(col2,col3)' are not leftmost prefixes of `(col1,col2,col3)'. *MySQL* also uses indexes for `LIKE' comparisons if the argument to `LIKE' is a constant string that doesn't start with a wildcard character. For example, the following `SELECT' statements use indexes: mysql> select * from tbl_name where key_col LIKE "Patrick%"; mysql> select * from tbl_name where key_col LIKE "Pat%_ck%"; In the first statement, only rows with `"Patrick" <= key_col < "Patricl"' are considered. In the second statement, only rows with `"Pat" <= key_col < "Pau"' are considered. The following `SELECT' statements will not use indexes: mysql> select * from tbl_name where key_col LIKE "%Patrick%"; mysql> select * from tbl_name where key_col LIKE other_col; In the first statement, the `LIKE' value begins with a wildcard character. In the second statement, the `LIKE' value is not a constant. How *MySQL* optimizes `WHERE' clauses ===================================== (This section is incomplete; *MySQL* does many optimizations.) In general, when you want to make a slow `SELECT ... WHERE' faster, the first thing to check is whether or not you can add an index. All references between different tables should usually be done with indexes. You can use the `EXPLAIN' command to determine which indexes are used for a `SELECT'. *Note Explain::. Some of the optimizations performed by *MySQL* are listed below: * Removal of unnecessary parentheses: ((a AND b) AND c OR (((a AND b) AND (c AND d)))) -> (a AND b AND c) OR (a AND b AND c AND d) * Constant folding: (a b>5 AND b=c AND a=5 * Constant condition removal (needed because of constant folding): (B>=5 AND B=5) OR (B=6 AND 5=5) OR (B=7 AND 5=6) -> B=5 OR B=6 * Constant expressions used by indexes are evaluated only once. * `COUNT(*)' on a single table without a `WHERE' is retrieved directly from the table information. This is also done for any `NOT NULL' expression when used with only one table. * Early detection of invalid constant expressions. *MySQL* quickly detects that some `SELECT' statements are impossible and returns no rows. * `HAVING' is merged with `WHERE' if you don't use `GROUP BY' or group functions (`COUNT()', `MIN()'...) * For each sub join, a simpler `WHERE' is constructed to get a fast `WHERE' evaluation for each sub join and also to skip records as soon as possible. * *MySQL* normally uses the index that finds least number of rows. An index is used for columns that you compare with the following operators: `=', `>', `>=', `<', `<=', `BETWEEN' and a `LIKE' with a non-wildcard prefix like `'something%''. * Any index that doesn't span all `AND' levels in the `WHERE' clause is not used to optimize the query. The following `WHERE' clauses use indexes: ... WHERE index_part1=1 AND index_part2=2 ... WHERE index=1 OR A=10 AND index=2 /* index = 1 OR index = 2 */ ... WHERE index_part1='hello' AND index_part_3=5 /* optimized like "index_part1='hello'" */ These `WHERE' clauses do *NOT* use indexes: ... WHERE index_part2=1 AND index_part3=2 /* index_part_1 is not used */ ... WHERE index=1 OR A=10 /* No index */ ... WHERE index_part1=1 OR index_part2=10 /* No index spans all rows */ * All constant tables are read first, before any other tables in the query. A constant table is: - An empty table or a table with 1 row. - A table that is used with a `WHERE' clause on a `UNIQUE' index or a `PRIMARY KEY', where all index parts are used with constant expressions. All the following tables are used as constant tables: mysql> SELECT * FROM t WHERE primary_key=1; mysql> SELECT * FROM t1,t2 WHERE t1.primary_key=1 AND t2.primary_key=t1.id; * The best join combination to join the tables is found by trying all possibilities :(. If all columns in `ORDER BY' and in `GROUP BY' come from the same table, then this table is preferred first when joining. * If there is an `ORDER BY' clause and a different `GROUP BY' clause, or if the `ORDER BY' or `GROUP BY' contains columns from tables other than the first table in the join queue, a temporary table is created. * Each table index is queried and the best index that spans less than 30% of the rows is used. If no such index can be found, a quick table scan is used. * In some cases, *MySQL* can read rows from the index without even consulting the data file. If all columns used from the index are numeric, then only the index tree is used to resolve the query. * Before each record is output, those that do not match the `HAVING' clause are skipped. Some examples of queries that are very fast: mysql> SELECT COUNT(*) FROM tbl_name; mysql> SELECT MIN(key_part1),MAX(key_part1) FROM tbl_name; mysql> SELECT MAX(key_part2) FROM tbl_name WHERE key_part_1=constant; mysql> SELECT ... FROM tbl_name ORDER BY key_part1,key_part2,... LIMIT 10; mysql> SELECT ... FROM tbl_name ORDER BY key_part1 DESC,key_part2 DESC,... LIMIT 10; The following queries are resolved using only the index tree (assuming the indexed columns are numeric): mysql> SELECT key_part1,key_part2 FROM tbl_name WHERE key_part1=val; mysql> SELECT COUNT(*) FROM tbl_name WHERE key_part1=val1 and key_part2=val2; mysql> SELECT key_part2 FROM tbl_name GROUP BY key_part1; The following queries use indexing to retrieve the rows in sorted order without a separate sorting pass: mysql> SELECT ... FROM tbl_name ORDER BY key_part1,key_part2,... mysql> SELECT ... FROM tbl_name ORDER BY key_part1 DESC,key_part2 DESC,... How *MySQL* opens and closes tables =================================== The cache of open tables can grow to a maximum of `table_cache' (default 64; this can be changed with with the `-O table_cache=#' option to `mysqld'). A table is never closed, except when the cache is full and another thread tries to open a table or if you use `mysqladmin refresh' or `mysqladmin flush-tables'. When the table cache fills up, the server uses the following procedure to locate a cache entry to use: * Tables that are not currently in use are released, in least-recently-used order. * If the cache is full and no tables can be released, but a new table needs to be opened, the cache is temporarily extended as necessary. * If the cache is in a temporarily-extended state and a table goes from in-use to not-in-use state, it is closed and released from the cache. A table is opened for each concurrent access. This means that if you have two threads accessing the same table or access the table twice in the same query (with `AS') the table needs to be opened twice. The first open of any table takes two file descriptors; each additional use of the table takes only one file descriptor. The extra descriptor for the first open is used for the index file; this descriptor is shared among all threads. Drawbacks of creating large numbers of tables in a database ----------------------------------------------------------- If you have many files in a directory, open, close and create operations will be slow. If you execute `SELECT' statements on many different tables, there will be a little overhead when the table cache is full, because for every table that has to be opened, another must be closed. You can reduce this overhead by making the table cache larger. Why so many open tables? ======================== When you run `mysqladmin status', you'll see something like this: Uptime: 426 Running threads: 1 Questions: 11082 Reloads: 1 Open tables: 12 This can be somewhat perplexing if you only have 6 tables. *MySQL* is multithreaded, so it may have many queries on the same table at once. To minimize the problem with two threads having different states on the same file, the table is opened independently by each concurrent thread. This takes some memory and one extra file descriptor for the data file. The index file descriptor is shared between all threads. Using symbolic links for databases and tables ============================================= You can move tables and databases from the database directory to other locations and replace them with symbolic links to the new locations. You might want to do this, for example, to move a database to a file system with more free space. If *MySQL* notices that a table is a symbolically-linked, it will resolve the symlink and use the table it points to instead. This works on all systems that support the `realpath()' call (at least Linux and Solaris support `realpath()')! On systems that don't support `realpath()', you should not access the table through the real path and through the symlink at the same time! If you do, the table will be inconsistent after any update. *MySQL* doesn't support linking of databases by default. Things will work fine as long as you don't make a symbolic link between databases. Suppose you have a database `db1' under the *MySQL* data directory, and then make a symlink `db2' that points to `db1': shell> cd /path/to/datadir shell> ln -s db1 db2 Now, for any table `tbl_a' in `db1', there also appears to be a table `tbl_a' in `db2'. If one thread updates `db1.tbl_a' and another thread updates `db2.tbl_a', there will be problems. If you really need this, you must change the following code in `mysys/mf_format.c': if (!lstat(to,&stat_buff)) /* Check if it's a symbolic link */ if (S_ISLNK(stat_buff.st_mode) && realpath(to,buff)) Change the code to this: if (realpath(to,buff)) How *MySQL* locks tables ======================== All locking in *MySQL* is deadlock-free. This is managed by always requesting all needed locks at once at the beginning of a query and always locking the tables in the same order. The locking method *MySQL* uses for `WRITE' locks works as follows: * If there are no locks on the table, put a write lock on it. * Otherwise, put the lock request in the write lock queue. The locking method *MySQL* uses for `READ' locks works as follows: * If there are no write locks on the table, put a read lock on it. * Otherwise, put the lock request in the read lock queue. When a lock is released, the lock is made available to the threads in the write lock queue, then to the threads in the read lock queue. This means that if you have many updates on a table, `SELECT' statements will wait until there are no more updates. To work around this for the case where you want to do many `INSERT' and `SELECT' operations on a table, you can insert rows in a temporary table and update the real table with the records from the temporary table once in a while. This can be done with the following code: mysql> LOCK TABLES real_table WRITE, insert_table WRITE; mysql> insert into real_table select * from insert_table; mysql> delete from insert_table; mysql> UNLOCK TABLES; You can use the `LOW_PRIORITY' or `HIGH_PRIORITY' options with `INSERT' if you want to prioritize retrieval in some specific cases. *Note Insert:: You could also change the locking code in `mysys/thr_lock.c' to use a single queue. In this case, write locks and read locks would have the same priority, which might help some applications. How to arrange a table to be as fast/small as possible ====================================================== You can get better performance on a table and minimize storage space using the techniques listed below: * Declare columns to be `NOT NULL' if possible. It makes everything faster and you save one bit per column. * Take advantage of the fact that all columns have default values. Insert values explicitly only when the value to be inserted differs from the default. You don't have to insert a value into the first `TIMESTAMP' column or into an `AUTO_INCREMENT' column in an `INSERT' statement. *Note `mysql_insert_id()': mysql_insert_id. * Use the smaller integer types if possible to get smaller tables. For example, `MEDIUMINT' is often better than `INT'. * If you don't have any variable-length columns (`VARCHAR', `TEXT' or `BLOB' columns), a fixed-size record format is used. This is much faster but unfortunately may waste some space. *Note Row format::. * To help *MySQL* optimize queries better, run `isamchk --analyze' on a table after it has been loaded with relevant data. This updates a value for each index that indicates the average number of rows that have the same value. (For unique indexes, this is always 1, of course.) * To sort an index and data according to an index, use `isamchk --sort-index --sort-records=1' (if you want to sort on index 1). If you have a unique index from which you want to read all records in order according to that index, this is a good way to make that faster. * For `INSERT' statements, use multiple value lists if possible. This is much faster than using separate `INSERT' statements. * When loading a table with data, use `LOAD DATA INFILE'. This is usually 20 times faster than using a lot of `INSERT' statements. *Note Load::. You can even get more speed when loading data into a table with many indexes using the following procedure: 1. Create the table in `mysql' or Perl with `CREATE TABLE'. 2. Execute `mysqladmin flush-tables'. 3. Use `isamchk --keys-used=0 /path/to/db/tbl_name'. This will remove all usage of all indexes from the table. 4. Insert data into the table with `LOAD DATA INFILE'. 5. If you have `pack_isam' and want to compress the table, run `pack_isam' on it. 6. Recreate the indexes with `isamchk -r -q /path/to/db/tbl_name'. 7. Execute `mysqladmin flush-tables'. * To get some more speed for both `LOAD DATA INFILE' and `INSERT', enlarge the key buffer. This can be done with the `-O key_buffer=#' option to `mysqld' or `safe_mysqld'. For example, 16M should be a good value if you have much RAM. :) * When dumping data as text files for use by other programs, use `SELECT ... INTO OUTFILE'. *Note Load::. * When doing many successive inserts or updates, you can get more speed by locking your tables using `LOCK TABLES'. `LOAD DATA INFILE' and `SELECT ...INTO OUTFILE' are atomic, so you don't have to use `LOCK TABLES' when using them. *Note Lock tables::. To check how fragmented your tables are, run `isamchk -evi' on the `.ISM' file. *Note Maintenance::. Factors affecting the speed of `INSERT' statements ================================================== The time to insert a record consists of: * Connect: (3) * Sending query to server: (2) * Parsing query: (2) * Inserting record: (1 x size of record) * Inserting indexes: (1 x indexes) * Close: (1) Where (number) is proportional time. This does not take into consideration the initial overhead to open tables (which is done once for each concurrently-running query). The size of the table slows down the insertion of indexes by N log N (B-trees). You can speed up insertions by locking your table and/or using multiple value lists with `INSERT' statements. Using multiple value lists can be up to 5 times faster than using separate inserts. mysql> LOCK TABLES a WRITE; mysql> INSERT INTO a VALUES (1,23),(2,34),(4,33); mysql> INSERT INTO a VALUES (8,26),(6,29); mysql> UNLOCK TABLES; The main speed difference is that the index buffer is flushed to disk only once, after all `INSERT' statements have completed. Normally there would be as many index buffer flushes as there are different `INSERT' statements. Locking is not needed if you can insert all rows with a single statement. Locking will also lower the total time of multi-connection tests, but the maximum wait time for some threads will go up (because they wait for locks). For example: thread 1 does 1000 inserts thread 2, 3, and 4 does 1 insert thread 5 does 1000 inserts If you don't use locking, 2, 3 and 4 will finish before 1 and 5. If you use locking, 2, 3 and 4 probably will not finish before 1 or 5, but the total time should be about 40% faster. As `INSERT', `UPDATE' and `DELETE' operations are very fast in *MySQL*, you will obtain better overall performance by adding locks around everything that does more than about 5 inserts or updates in a row. If you do very many inserts in a row, you could do a `LOCK TABLES' followed by a `UNLOCK TABLES' once in a while (about each 1000 rows) to allow other threads access to the table. This would still result in a nice performance gain. Of course, `LOAD DATA INFILE' is much faster still. Factors affecting the speed of `DELETE' statements ================================================== The time to delete a record is exactly proportional to the number of indexes. To delete records more quickly, you can increase the size of the index cache. The default index cache is 1M; to get faster deletes, it should be increased by several factors (try 16M if you have enough memory). How do I get *MySQL* to run at full speed? ========================================== Start by benchmarking your problem! You can take any program from the *MySQL* benchmark suite (normally found in the `sql-bench' directory) and modify it for your needs. By doing this, you can try different solutions to your problem and test which is really the fastest solution for you. * Start `mysqld' with the correct options. More memory gives more speed if you have it. *Note *MySQL* parameters: MySQL parameters. * Create indexes to make your `SELECT' statements faster. *Note *MySQL* indexes: MySQL indexes. * Optimize your column types to be as efficient as possible. For example, declere columns to be `NOT NULL' if possible. *Note Table efficiency::. * The `--skip-locking' option disables file locking between SQL requests. This gives greater speed but has the following consequences: - You *MUST* flush all tables with `mysqladmin flush-tables' before you try to check or repair tables with `isamchk'. (`isamchk -d tbl_name' is always allowed, since that simply displays table information.) - You can't run two *MySQL* servers on the same data files, if both are going to update the same tables. The `--skip-locking' option is on by default when compiling with MIT-pthreads, because `flock()' isn't fully supported by MIT-pthreads on all platforms. * If updates are a problem, you can delay updates and then do many updates in a row later. Doing many updates in a row is much quicker than doing one at a time. * On FreeBSD systems, if the problem is with MIT-pthreads, upgrading to FreeBSD 3.0 (or higher) should help. This makes it possible to use Unix sockets (with FreeBSD, this is quicker than connecting using TCP/IP with MIT-pthreads) and the threads package is much more integrated. * `GRANT' checking on the table or column level will decrease performance. What are the different row formats? Or, when should `VARCHAR/CHAR' be used? =========================================================================== *MySQL* dosen't have true SQL `VARCHAR' types. Instead, *MySQL* has three different ways to store records and uses these to emulate `VARCHAR'. If a table doesn't have any `VARCHAR', `BLOB' or `TEXT' columns, a fixed row size is used. Otherwise a dynamic row size is used. `CHAR' and `VARCHAR' columns are treated identically from the application's point of view; both have trailing spaces removed when the columns are retrieved. You can check the format used in a table with `isamchk -d' (`-d' means "describe the table"). *MySQL* has three different table formats: fixed-length, dynamic and compressed. These are compared below. *Fixed-length tables* * This is the default format. It's used when the table contains no `VARCHAR', `BLOB' or `TEXT' columns. * All `CHAR', `NUMERIC' and `DECIMAL' columns are space-padded to the column width. * Very quick. * Easy to cache. * Easy to reconstruct after a crash, because records are located in fixed positions. * Doesn't have to be reorganized (with `isamchk') unless a huge number of records are deleted and you want to return free disk space to the operating system. * Usually requires more disk space than dynamic tables. *Dynamic tables* * This format is used if the table contains any `VARCHAR', `BLOB' or `TEXT' columns. * All string columns are dynamic (except those with a length less than 4). * Each record is preceded by a bitmap indicating which columns are empty (`''') for string columns, or zero for numeric columns (this isn't the same as columns containing `NULL' values). If a string column has a length of zero after removal of trailing spaces, or a numeric column has a value of zero, it is marked in the bit map and not saved to disk. Non-empty strings are saved as a length byte plus the string contents. * Usually takes much less disk space than fixed-length tables. * Each record uses only as much space as is required. If a record becomes larger, it is split into as many pieces as required. This results in record fragmentation. * If you update a row with information that extends the row length, the row will be fragmented. In this case, you may have to run `isamchk -r' from time to time to get better performance. Use `isamchk -ei tbl_name' for some statistics. * Not as easy to reconstruct after a crash, because a record may be fragmented into many pieces and a link (fragment) may be missing. * The expected row length for dynamic sized records is: 3 + (number of columns + 7) / 8 + (number of char columns) + packed size of numeric columns + length of strings + (number of NULL columns + 7) / 8 There is a penalty of 6 bytes for each link. A dynamic record is linked whenever an update causes an enlargement of the record. Each new link will be at least 20 bytes, so the next enlargement will probably go in the same link. If not, there will be another link. You may check how many links there are with `isamchk -ed'. All links may be removed with `isamchk -r'. *Compressed tables* * A read-only table made with the `pack_isam' utility. All customers with extended *MySQL* email support are entitled to a copy of `pack_isam' for their internal usage. * The uncompress code exists in all *MySQL* distributions so that even customers who don't have `pack_isam' can read tables that were compressed with `pack_isam' (as long as the table was compressed on the same platform). * Takes very little disk space. Minimises disk usage. * Each record is compressed separately (very little access overhead). The header for a record is fixed (1-3 bytes) depending on the biggest record in the table. Each column is compressed differently. Some of the compression types are: - There is usually a different Huffman table for each column. - Suffix space compression. - Prefix space compression. - Numbers with value `0' are stored using 1 bit. - If values in an integer column have a small range, the column is stored using the smallest possible type. For example, a `BIGINT' column (8 bytes) may be stored as a `TINYINT' column (1 byte) if all values are in the range `0' to `255'. - If a column has only a small set of possible values, the column type is converted to `ENUM'. - A column may use a combination of the above compressions. * Can handle fixed or dynamic length records, but not `BLOB' or `TEXT' columns. * Can be uncompressed with `isamchk'. *MySQL* can support different index types, but the normal type is NISAM. This is a B-tree index and you can roughly calculate the size for the index file as `(key_length+4)*0.67', summed over all keys. (This is for the worst case when all keys are inserted in sorted order.) String indexes are space compressed. If the first index part is a string, it will also be prefix compressed. Space compression makes the index file smaller if the string column has a lot of trailing space or is a `VARCHAR' column that is not always used to the full length. Prefix compression helps if there are many strings with an identical prefix. The *MySQL* benchmark suite *************************** This should contain a technical description of the *MySQL* benchmark suite (and `crash-me') but that description is not written yet. Currently, you should look at the code and results in the `bench' directory in the distribution (and of course on the web page at `http://www.tcx.se/crash-me-choose.htmy'). It is meant to be a benchmark that will tell any user what things a given SQL implementation performs well or poorly at. `crash-me' tries to determine what features a database supports and what its capabilities and limitations are by actually running queries. For example, it determines: * What column types are supported * How many indexes are supported * What functions are supported * How big a query can be * How big a `VARCHAR' column can be *MySQL* Utilites **************** Overview of the different *MySQL* programs ========================================== All *MySQL* clients that communicate with the server using the `mysqlclient' library use the following environment variables: *Name* *Description* `MYSQL_UNIX_PORT' The default socket; used for connections to `localhost' `MYSQL_TCP_PORT' The default TCP/IP port `MYSQL_PWD' The default password `MYSQL_DEBUG' Debug-trace options when debugging `TMPDIR' The directory where temporary tables/files are created Use of `MYSQL_PWD' is insecure. *Note Connecting::. The `mysql' client uses the file named in the `MYSQL_HISTFILE' environment variable to save the command line history. The default value for the history file is `$HOME/.mysql_history', where `$HOME' is the value of the `HOME' environment variable. All *MySQL* programs take many different options. However, every *MySQL* program provides a `--help' option that you can use to get a full description of the program's different options. For example, try `mysql --help'. The list below briefly describes the *MySQL* programs: `isamchk' Utility to describe, check, optimize and repair *MySQL* tables. Because `isamchk' has many functions, it is described in its own chapter. *Note Maintenance::. `make_binary_release' Makes a binary release of a compiled *MySQL*. This could be sent by FTP to `/pub/mysql/Incoming' on `ftp.tcx.se' for the convenience of other *MySQL* users. `msql2mysql' A shell script that converts `mSQL' programs to *MySQL*. It doesn't handle all cases, but it gives a good start when converting. `mysql' `mysql' is a simple SQL shell (with GNU `readline' capabilities). It supports interactive and non-interactive use. When used interactively, query results are presented in an ASCII-table format. When used non-interactively (e.g., as a filter), the result is presented in tab-separated format. (The output format can be changed using command-line options.) You can run scripts simply like this: shell> mysql database < script.sql > output.tab If you have problems due to insufficient memory in the client, use the `--quick' option! This forces `mysql' to use `mysql_use_result()' rather than `mysql_store_result()' to retrieve the result set. `mysqlaccess' A script that checks the access privileges for a host, user and database combination. `mysqladmin' Utility for performing administrative operations, such as creating or dropping databases, reloading the grant tables, flushing tables to disk and reopening log files. `mysqladmin' can also be used to retrieve version, process and status information from the server. `mysqlbug' The *MySQL* bug report script. This script should always be used when filing a bug report to the *MySQL* list. `mysqld' The SQL daemon. This should always be running. `mysqldump' Dumps a *MySQL* database into a file as SQL statements or as tab-separated text files. Enhanced freeware originally by Igor Romanenko. `mysqlimport' Imports text files into their respective tables using `LOAD DATA INFILE'. *Note `mysqlimport': mysqlimport. `mysqlshow' Displays information about databases, tables, columns and indexes. `mysql_install_db' Creates the *MySQL* grant tables with default privileges. This is usually executed only once, when first installing *MySQL* on a system. `replace' A utility program that is used by `msql2mysql', but that has more general applicability as well. `replace' changes strings in place in files or on the standard input. Uses a finite state machine to match longer strings first. Can be used to swap strings. For example, this command swaps `a' and `b' in the given files: shell> replace a b b a -- file1 file2 ... `safe_mysqld' A script that starts the `mysqld' daemon with some safety features, such as restarting the server when an error occurs and logging runtime information to a log file. Importing data from text files ============================== `mysqlimport' provides a command line interface to the `LOAD DATA INFILE' SQL statement. Most options to `mysqlimport' correspond directly to the same options to `LOAD DATA INFILE'. *Note Load::. `mysqlimport' is invoked like this: shell> mysqlimport [options] filename ... For each text file named on the command line, `mysqlimport' strips any extension from the filename and uses the result to determine which table to import the file's contents into. For example, files named `patient.txt', `patient.text' and `patient' would all be imported into a table named `patient'. `mysqlimport' supports the following options: `-C, --compress' Compress all information between the client and the server if both support compression. `-#, --debug[=option_string]' Trace usage of the program (for debugging). `-d, --delete' Empty the table before importing the text file. `--fields-terminated-by=...' `--fields-enclosed-by=...' `--fields-optionally-enclosed-by=...' `--fields-escaped-by=...' `--fields-terminated-by=...' These options have the same meaning as the corresponding clauses for `LOAD DATA INFILE'. `-f, --force' Ignore errors. For example, if a table for a text file doesn't exist, continue processing any remaining files. Without `--force', `mysqlimport' exits if a table doesn't exist. `--help' Display a help message and exit. `-h host_name, --host=host_name' Import data to the *MySQL* server on the named host. The default host is `localhost'. `-i, --ignore' See the description for the `--replace' option. `-l, --lock-tables' Lock *ALL* tables for writing before processing any text files. This ensures that all tables are synchronized on the server. `-L, --local' Read input files from the client. By default, text files are assumed to be on the server if you connect to `localhost' (which is the default host). `-pyour_pass, --password[=your_pass]' The password to use when connecting to the server. If you specify no `=your_pass' part, `mysqlimport' solicits the password from the terminal. `-P port_num, --port=port_num' The TCP/IP port number to use for connecting to a host. (This is used for connections to hosts other than `localhost', for which Unix sockets are used.) `-r, --replace' The `--replace' and `--ignore' options control handling of input records that duplicate existing records on unique key values. If you specify `--replace', new rows replace existing rows that have the same unique key value. If you specify `--ignore', input rows that duplicate an existing row on a unique key value are skipped. If you don't specify either option, an error occurs when a duplicate key value is found, and the rest of the text file is ignored. `-s, --silent' Silent mode. Write output only when errors occur. `-S /path/to/socket, --socket=/path/to/socket' The socket file to use when connecting to `localhost' (which is the default host). `-u user_name, --user=user_name' The *MySQL* user name to use when connecting to the server. The default value is your Unix login name. `-v, --verbose' Verbose mode. Print out more information what the program does. `-V, --version' Print version information and exit. The *MySQL* compressed read-only table generator ================================================ `pack_isam' is an extra utility that you get when you order more than 10 licenses or extended support. Since `pack_isam' is distributed only in binary form, `pack_isam' is available only on some platforms. Of course, all future updates to `pack_isam' are included in the price. `pack_isam' may at some time be included as standard when we get some kind of turnover for *MySQL*. `pack_isam' works by compressing each column in the table separately. The information needed to decompress columns is read into memory when the table is opened. This results in much better performance when accessing individual records, since you only have to uncompress exactly one record, not a much larger disk block like when using Stacker on MS-DOS. Usually, `pack_isam' packs the data file 40%-70%. *MySQL* uses memory mapping (`mmap()') on compressed tables and falls back to normal read/write file usage if `mmap()' doesn't work. There are currently two limitations with `pack_isam': * After packing, the table is read only. * It can't pack `BLOB' columns, yet. Fixing these limitations is on our TODO list but with low priority. `pack_isam' is invoked like this: shell> pack_isam [options] filename ... Each filename should be the name of an index (`.ISM') file. If you are not in the database directory, you should specify the pathname to the file. It is permissible to omit the `.ISM' extension. `pack_isam' supports the following options: `-b, --backup' Make a backup of the table as `tbl_name.OLD'. `-#, --debug=debug_options' Output debug log. The `debug_options' string often is `'d:t:o,filename''. `-f, --force' Force packing of the table even if it becomes bigger or if the temporary file exists. (`pack_isam' creates a temporary file named `tbl_name.TMD' while it compresses the table. If you kill `pack_isam', the `.TMD' file may not be deleted. Normally, `pack_isam' exits with an error if it finds that `tbl_name.TMD' exists. With `--force', `pack_isam' packs the table anyway. `-?, --help' Display a help message and exit. `-j big_tbl_name, --join=big_tbl_name' Join all tables named on the command line into a single table `big_tbl_name'. All tables that are to be combined MUST be identical (same column names and types, same indexes, etc.) `-p #, --packlength=#' Specify the record length storage size, in bytes. The value should be 1, 2 or 3. (`pack_isam' stores all rows with length pointers of 1, 2 or 3 bytes. In most normal cases, `pack_isam' can determine the right length value before it begins packing the file, but it may notice during the packing process that it could have used a shorter length. In this case, `pack_isam' will print a note that the next time you pack the same file, you could use a shorter record length.) `-s, --silent' Silent mode. Write output only when errors occur. `-t, --test' Don't pack table, only test packing it. `-T dir_name, --tmp_dir=dir_name' Use the named directory as the location in which to write the temporary table. `-v, --verbose' Verbose mode. Write info about progress and packing result. `-V, --version' Display version information and exit. `-w, --wait' Wait and retry if table is in use. If the `mysqld' server was invoked with the `--skip-locking' option, it is not a good idea to invoke `pack_isam' if the table might be updated during the packing process. The sequence of commands shown below illustrates a typical table compression session: shell> ls -l station.* -rw-rw-r-- 1 monty my 994128 Apr 17 19:00 station.ISD -rw-rw-r-- 1 monty my 53248 Apr 17 19:00 station.ISM -rw-rw-r-- 1 monty my 5767 Apr 17 19:00 station.frm shell> isamchk -dvv station ISAM file: station Isam-version: 2 Creation time: 1996-03-13 10:08:58 Recover time: 1997-02-02 3:06:43 Data records: 1192 Deleted blocks: 0 Datafile: Parts: 1192 Deleted data: 0 Datafile pointer (bytes): 2 Keyfile pointer (bytes): 2 Max datafile length: 54657023 Max keyfile length: 33554431 Recordlength: 834 Record format: Fixed length table description: Key Start Len Index Type Root Blocksize Rec/key 1 2 4 unique unsigned long 1024 1024 1 2 32 30 multip. text 10240 1024 1 Field Start Length Type 1 1 1 2 2 4 3 6 4 4 10 1 5 11 20 6 31 1 7 32 30 8 62 35 9 97 35 10 132 35 11 167 4 12 171 16 13 187 35 14 222 4 15 226 16 16 242 20 17 262 20 18 282 20 19 302 30 20 332 4 21 336 4 22 340 1 23 341 8 24 349 8 25 357 8 26 365 2 27 367 2 28 369 4 29 373 4 30 377 1 31 378 2 32 380 8 33 388 4 34 392 4 35 396 4 36 400 4 37 404 1 38 405 4 39 409 4 40 413 4 41 417 4 42 421 4 43 425 4 44 429 20 45 449 30 46 479 1 47 480 1 48 481 79 49 560 79 50 639 79 51 718 79 52 797 8 53 805 1 54 806 1 55 807 20 56 827 4 57 831 4 shell> pack_isam station.ISM Compressing station.ISM: (1192 records) - Calculating statistics normal: 20 empty-space: 16 empty-zero: 12 empty-fill: 11 pre-space: 0 end-space: 12 table-lookups: 5 zero: 7 Original trees: 57 After join: 17 - Compressing file 87.14% shell> ls -l station.* -rw-rw-r-- 1 monty my 127874 Apr 17 19:00 station.ISD -rw-rw-r-- 1 monty my 55296 Apr 17 19:04 station.ISM -rw-rw-r-- 1 monty my 5767 Apr 17 19:00 station.frm shell> isamchk -dvv station ISAM file: station Isam-version: 2 Creation time: 1996-03-13 10:08:58 Recover time: 1997-04-17 19:04:26 Data records: 1192 Deleted blocks: 0 Datafile: Parts: 1192 Deleted data: 0 Datafilepointer (bytes): 3 Keyfile pointer (bytes): 1 Max datafile length: 16777215 Max keyfile length: 131071 Recordlength: 834 Record format: Compressed table description: Key Start Len Index Type Root Blocksize Rec/key 1 2 4 unique unsigned long 10240 1024 1 2 32 30 multip. text 54272 1024 1 Field Start Length Type Huff tree Bits 1 1 1 constant 1 0 2 2 4 zerofill(1) 2 9 3 6 4 no zeros, zerofill(1) 2 9 4 10 1 3 9 5 11 20 table-lookup 4 0 6 31 1 3 9 7 32 30 no endspace, not_always 5 9 8 62 35 no endspace, not_always, no empty 6 9 9 97 35 no empty 7 9 10 132 35 no endspace, not_always, no empty 6 9 11 167 4 zerofill(1) 2 9 12 171 16 no endspace, not_always, no empty 5 9 13 187 35 no endspace, not_always, no empty 6 9 14 222 4 zerofill(1) 2 9 15 226 16 no endspace, not_always, no empty 5 9 16 242 20 no endspace, not_always 8 9 17 262 20 no endspace, no empty 8 9 18 282 20 no endspace, no empty 5 9 19 302 30 no endspace, no empty 6 9 20 332 4 always zero 2 9 21 336 4 always zero 2 9 22 340 1 3 9 23 341 8 table-lookup 9 0 24 349 8 table-lookup 10 0 25 357 8 always zero 2 9 26 365 2 2 9 27 367 2 no zeros, zerofill(1) 2 9 28 369 4 no zeros, zerofill(1) 2 9 29 373 4 table-lookup 11 0 30 377 1 3 9 31 378 2 no zeros, zerofill(1) 2 9 32 380 8 no zeros 2 9 33 388 4 always zero 2 9 34 392 4 table-lookup 12 0 35 396 4 no zeros, zerofill(1) 13 9 36 400 4 no zeros, zerofill(1) 2 9 37 404 1 2 9 38 405 4 no zeros 2 9 39 409 4 always zero 2 9 40 413 4 no zeros 2 9 41 417 4 always zero 2 9 42 421 4 no zeros 2 9 43 425 4 always zero 2 9 44 429 20 no empty 3 9 45 449 30 no empty 3 9 46 479 1 14 4 47 480 1 14 4 48 481 79 no endspace, no empty 15 9 49 560 79 no empty 2 9 50 639 79 no empty 2 9 51 718 79 no endspace 16 9 52 797 8 no empty 2 9 53 805 1 17 1 54 806 1 3 9 55 807 20 no empty 3 9 56 827 4 no zeros, zerofill(2) 2 9 57 831 4 no zeros, zerofill(1) 2 9 The information printed by `pack_isam' is described below: `normal' The number of columns for which no extra packing is used. `empty-space' The number of columns containing values that are only spaces; these will occupy 1 bit. `empty-zero' The number of columns containing values that are only binary 0's; these will occupy 1 bit. `empty-fill' The number of integer columns that don't occupy the full byte range of their type; these are changed to a smaller type (for example, an `INTEGER' column may be changed to `MEDIUMINT'). `pre-space' The number of decimal columns that are stored with leading space. In this case, each value will contain a count for the number of leading spaces. `end-space' The number of columns that have a lot of trailing space. In this case, each value will contain a count for the number of trailing spaces. `table-lookup' The column had only a small number of different values, and that were converted to an `ENUM' before Huffman compression. `zero' The number of columns for which all values are zero. `Original trees' The initial number of Huffman trees. `After join' The number of distinct Huffman trees left after joining trees to save some header space. After a table has been compressed, `isamchk -dvv' prints additional information about each field: `Type' The field type may contain the following descriptors: `constant' All rows have the same value. `no endspace' Don't store endspace. `no endspace, not_always' Don't store endspace and don't do end space compression for all values. `no endspace, no empty' Don't store endspace. Don't store empty values. `table-lookup' The column was converted to an `ENUM'. `zerofill(n)' The most significant `n' bytes in the value are always 0 and are not stored. `no zeros' Don't store zeros. `always zero' 0 values are stored in 1 bit. `Huff tree' The Huffman tree associated with the field `Bits' The number of bits used in the Huffman tree. Using `isamchk' for table maintenance and crash recovery ******************************************************** You can use the `isamchk' utility to get information about your database tables, check and repair them or optimize them. The following sections describe how to invoke `isamchk' (including a description of its options), how to set up a table maintenance schedule, and how to use `isamchk' to perform its various functions. `isamchk' invocation syntax =========================== `isamchk' is invoked like this: shell> isamchk [options] tbl_name The `options' specify what you want `isamchk' to do. They are described below. (You can also get a list of options by invoking `isamchk --help'.) With no options, `isamchk' simply checks your table. To get more information or to tell `isamchk' to take corrective action, specify options as described below and in the following sections. `tbl_name' is the database table you want to check. If you run `isamchk' somewhere other than in the database directory, you must specify the path to the file, since `isamchk' has no idea where your database is located. Actually, `isamchk' doesn't care whether or not the files you are working on are located in a database directory; you can copy the files that correspond to a database table into another location and perform recovery operations on them there. You can name several tables on the `isamchk' command line if you wish. You can also specify a name as an index file name (with the `.ISM' suffix), which allows you to specify all tables in a directory by using the pattern `*.ISM'. For example, if you are in a database directory, you can check all the tables in the directory like this: shell> isamchk *.ISM If you are not in the database directory, you can check all the tables there by specifying the path to the directory: shell> isamchk /path/to/database_dir/*.ISM You can even check all tables in all databases by specifying a wildcard with the path to the *MySQL* data directory: shell> isamchk /path/to/datadir/*/*.ISM `isamchk' supports the following options: `-a, --analyze' Analyze the distribution of keys. This will make some joins in *MySQL* faster. `-#, --debug=debug_options' Output debug log. The `debug_options' string often is `'d:t:o,filename''. `-d, --description' Prints some information about the table. `-e, --extend-check' Check the table VERY thoroughly. This is necessary only in extreme cases. Normally, `isamchk' should find all errors even without this option. `-f, --force' Overwrite old temporary files. If you use `-f' when checking tables (running `isamchk' without `-r'), `isamchk' will automatically restart with `-r' on any table for which an error occurs during checking. `--help' Display a help message and exit. `-i, --information' Print informational statistics about the table that is checked. `-k #, --keys-used=#' Used with `-r'. Tell the NISAM table handler to update only the first `#' indexes. Higher-numbered indexes are deactivated. This can be used to get faster inserts! Deactivated indexes can be reactivated by using `isamchk -r'. `-l, --no-symlinks' Do not follow symbolic links when repairing. Normally `isamchk' repairs the table a symlink points at. `-q, --quick' Used with `-r' to get a faster repair. Normally, the original data file isn't touched; you can specify a second `-q' to force the original data file to be used. `-r, --recover' Recovery mode. Can fix almost anything except unique keys that aren't unique. `-o, --safe-recover' Recovery mode. Uses an old recovery method; this is slower than `-r', but can handle a couple of cases that `-r' cannot handle. `-O var=option, --set-variable var=option' Set the value of a variable. The possible variables are listed below. `-s, --silent' Silent mode. Write output only when errors occur. You can use `-s' twice (`-ss') to make `isamchk' very silent. `-S, --sort-index' Sort index blocks. This speeds up "read-next" in applications. `-R index_num, --sort-records=index_num' Sort records according to an index. This makes your data much more localized and may speed up ranged `SELECT' and `ORDER BY' operations on this index. (It may be VERY slow to do a sort the first time!) To find out a table's index numbers, use `SHOW INDEX', which shows a table's indexes in the same order that `isamchk' sees them. Indexes are numbered beginning with 1. `-u, --unpack' Unpack a table that was packed with `pack_isam'. `-v, --verbose' Verbose mode. Print more information. This can be used with `-d' and `-e'. Use `-v' multiple times (`-vv', `-vvv') for more verbosity! `-V, --version' Print the `isamchk' version and exit. `-w, --wait' Wait if the table is locked. Possible variables for the `--set-variable' (`-O') option are: keybuffer default value: 520192 readbuffer default value: 262136 writebuffer default value: 262136 sortbuffer default value: 2097144 sort_key_blocks default value: 16 decode_bits default value: 9 `isamchk' memory usage ====================== Memory allocation is important when you run `isamchk'. `isamchk' uses no more memory than you specify with the `-O' options. If you are going to use `isamchk' on very large files, you should first decide how much memory you want it to use. The default is to use only about 3M to fix things. By using larger values, you can get `isamchk' to operate faster. For example, if you have more than 32M RAM, you could use options such as these (in addition to any other options you might specify): shell> isamchk -O sortbuffer=16M -O keybuffer=16M \ -O readbuffer=1M -O writebuffer=1M ... Using `-O sortbuffer=16M' should probably be enough for most cases. Be aware that `isamchk' uses temporary files in `TMPDIR'. If `TMPDIR' points to a memory file system, you may easily get out of memory errors. Setting up a table maintenance regime ===================================== It is a good idea to perform table checks on a regular basis rather than waiting for problems to occur. For maintenance purposes, you can use `isamchk -s' to check tables. The `-s' option causes `isamchk' to run in silent mode, printing messages only when errors occur. It's a good idea to check tables when the server starts up. For example, whenever the machine has done a reboot in the middle of an update, you usually need to check all the tables that could have been affected. (This is an "expected crashed table".) You could add a test to `safe_mysqld' that runs `isamchk' to check all tables that have been modified during the last 24 hours if there is an old `.pid' (process ID) file left after a reboot. (The `.pid' file is created by `mysqld' when it starts up and removed when it terminates normally. The presence of a `.pid' file at system startup time indicates that `mysqld' terminated abnormally.) An even better test would be to check any table whose last-modified time is more recent than that of the `.pid' file. You should also check your tables regularly during normal system operation. At TcX, we run a `cron' job to check all our important tables once a week, using a line like this in a `crontab' file: 35 0 * * 0 /path/to/isamchk -s /path/to/datadir/*/*.ISM This prints out information about crashed tables so we can examine and repair them when needed. As we haven't had any unexpectedly crashed tables (tables that become corrupted for reasons other than hardware trouble) for a couple of years now (this is really true), once a week is more than enough for us. We recommend that to start with, you execute `isamchk -s' each night on all tables that have been updated during the last 24 hours, until you come to trust *MySQL* as much as we do. Getting information about a table ================================= To get a description of a table or statistics about it, use the commands shown below. We explain some of the information in more detail later. `isamchk -d tbl_name' Runs `isamchk' in "describe mode" to produce a description of your table. If you start the *MySQL* server using the `--skip-locking' option, `isamchk' may report an error for a table that is updated while it runs. However, since `isamchk' doesn't change the table in describe mode, there isn't any risk of destroying data. `isamchk -d -v tbl_name' To produce more information about what `isamchk' is doing, add `-v' to tell it to run in verbose mode. `isamchk -eis tbl_name' Shows only the most important information from a table. It is slow since it must read the whole table. `isamchk -eiv tbl_name' This is like `-eis', but tells you what is being done. Example of `isamchk -d' output: ISAM file: company.ISM Data records: 1403698 Deleted blocks: 0 Recordlength: 226 Record format: Fixed length table description: Key Start Len Index Type 1 2 8 unique double 2 15 10 multip. text packed stripped 3 219 8 multip. double 4 63 10 multip. text packed stripped 5 167 2 multip. unsigned short 6 177 4 multip. unsigned long 7 155 4 multip. text 8 138 4 multip. unsigned long 9 177 4 multip. unsigned long 193 1 text Example of `isamchk -d -v' output: ISAM file: company.ISM Isam-version: 2 Creation time: 1996-08-28 11:44:22 Recover time: 1997-01-12 18:35:29 Data records: 1403698 Deleted blocks: 0 Datafile: Parts: 1403698 Deleted data: 0 Datafilepointer (bytes): 3 Keyfile pointer (bytes): 3 Max datafile length: 3791650815 Max keyfile length: 4294967294 Recordlength: 226 Record format: Fixed length table description: Key Start Len Index Type Root Blocksize Rec/key 1 2 8 unique double 15845376 1024 1 2 15 10 multip. text packed stripped 25062400 1024 2 3 219 8 multip. double 40907776 1024 73 4 63 10 multip. text packed stripped 48097280 1024 5 5 167 2 multip. unsigned short 55200768 1024 4840 6 177 4 multip. unsigned long 65145856 1024 1346 7 155 4 multip. text 75090944 1024 4995 8 138 4 multip. unsigned long 85036032 1024 87 9 177 4 multip. unsigned long 96481280 1024 178 193 1 text Example of `isamchk -eis' output: Checking ISAM file: company.ISM Key: 1: Keyblocks used: 97% Packed: 0% Max levels: 4 Key: 2: Keyblocks used: 98% Packed: 50% Max levels: 4 Key: 3: Keyblocks used: 97% Packed: 0% Max levels: 4 Key: 4: Keyblocks used: 99% Packed: 60% Max levels: 3 Key: 5: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 6: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 7: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 8: Keyblocks used: 99% Packed: 0% Max levels: 3 Key: 9: Keyblocks used: 98% Packed: 0% Max levels: 4 Total: Keyblocks used: 98% Packed: 17% Records: 1403698 M.recordlength: 226 Packed: 0% Recordspace used: 100% Empty space: 0% Blocks/Record: 1.00 Recordblocks: 1403698 Deleteblocks: 0 Recorddata: 317235748 Deleted data: 0 Lost space: 0 Linkdata: 0 User time 1626.51, System time 232.36 Maximum resident set size 0, Integral resident set size 0 Non physical pagefaults 0, Physical pagefaults 627, Swaps 0 Blocks in 0 out 0, Messages in 0 out 0, Signals 0 Voluntary context switches 639, Involuntary context switches 28966 Example of `isamchk -eiv' output: Checking ISAM file: company.ISM Data records: 1403698 Deleted blocks: 0 - check file-size - check delete-chain index 1: index 2: index 3: index 4: index 5: index 6: index 7: index 8: index 9: No recordlinks - check index reference - check data record references index: 1 Key: 1: Keyblocks used: 97% Packed: 0% Max levels: 4 - check data record references index: 2 Key: 2: Keyblocks used: 98% Packed: 50% Max levels: 4 - check data record references index: 3 Key: 3: Keyblocks used: 97% Packed: 0% Max levels: 4 - check data record references index: 4 Key: 4: Keyblocks used: 99% Packed: 60% Max levels: 3 - check data record references index: 5 Key: 5: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 6 Key: 6: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 7 Key: 7: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 8 Key: 8: Keyblocks used: 99% Packed: 0% Max levels: 3 - check data record references index: 9 Key: 9: Keyblocks used: 98% Packed: 0% Max levels: 4 Total: Keyblocks used: 9% Packed: 17% - check records and index references [LOTS OF ROW NUMBERS DELETED] Records: 1403698 M.recordlength: 226 Packed: 0% Recordspace used: 100% Empty space: 0% Blocks/Record: 1.00 Recordblocks: 1403698 Deleteblocks: 0 Recorddata: 317235748 Deleted data: 0 Lost space: 0 Linkdata: 0 User time 1639.63, System time 251.61 Maximum resident set size 0, Integral resident set size 0 Non physical pagefaults 0, Physical pagefaults 10580, Swaps 0 Blocks in 4 out 0, Messages in 0 out 0, Signals 0 Voluntary context switches 10604, Involuntary context switches 122798 Here are the sizes of the data and index files for the table used in the preceding examples: -rw-rw-r-- 1 monty tcx 317235748 Jan 12 17:30 company.ISD -rw-rw-r-- 1 davida tcx 96482304 Jan 12 18:35 company.ISM Explanations for the types of information `isamchk' produces are given below. The "keyfile" is the index file. "Record" and "row" are synonymous. `ISAM file' Name of the ISAM (index) file. `Isam-version' Version of ISAM format. Currently always 2. `Creation time' When the data file was created. `Recover time' When the index/data file was last reconstructed. `Data records' How many records are in the table. `Deleted blocks' How many deleted blocks still have reserved space. You can optimize your table to minimize this space. *Note Optimization::. `Datafile: Parts' For dynamic record format, this indicates how many data blocks there are. For an optimized table without fragmented records, this is the same as `Data records'. `Deleted data' How many bytes of non-reclaimed deleted data there are. You can optimize your table to minimize this space. *Note Optimization::. `Datafile pointer' The size of the data file pointer, in bytes. It is usually 2, 3, 4 or 5 bytes. Most tables manage with 2 bytes, but this cannot be controlled from *MySQL* yet. For fixed tables, this is a record address. For dynamic tables, this is a byte address. `Keyfile pointer' The size of the index file pointer, in bytes. It is usually 1, 2 or 3 bytes. Most tables manage with 2 bytes, but this is calculated automatically by *MySQL*. It is always a block address. `Max datafile length' How long the table's data file (`.ISD' file) can become, in bytes. `Max keyfile length' How long the table's key file (`.ISM' file) can become, in bytes. `Recordlength' How much space each record takes, in bytes. `Record format' The format used to store table rows. The examples shown above use `Fixed length'. Other possible values are `Compressed' and `Packed'. `table description' A list of all keys in the table. For each key, some low-level information is presented: `Key' This key's number. `Start' Where in the record this index part starts. `Len' How long this index part is. For packed numbers, this should always be the full length of the column. For strings, it may be shorter than the full length of the indexed column, because you can index a prefix of a string column. `Index' `unique' or `multip.' (multiple). Indicates whether or not one value can exist multiple times in this index. `Type' What data-type this index part has. This is an NISAM data-type with the options `packed', `stripped' or `empty'. `Root' Address of the root index block. `Blocksize' The size of each index block. By default this is 1024, but the value may be changed at compile time. `Rec/key' This is a statistical value used by the optimizer. It tells how many records there are per value for this key. A unique key always has a value of 1. This may be updated after a table is loaded (or greatly changed) with `isamchk -a'. If this is not updated at all, a default value of 30 is given. `' In the first example above, the 9th key is a multi-part key with two parts. `Keyblocks used' What percentage of the keyblocks are used. Since the table used in the examples had just been reorganized with `isamchk', the values are very high (very near the theoretical maximum). `Packed' *MySQL* tries to pack keys with a common suffix. This can only be used for `CHAR'/`VARCHAR'/`DECIMAL' keys. For long strings like names, this can significantly reduce the space used. In the third example above, the 4th key is 10 characters long and a 60% reduction in space is achieved. `Max levels' How deep the B-tree for this key is. Large tables with long keys get high values. `Records' How many rows are in the table. `M.recordlength' The average record length. For tables with fixed-length records, this is the exact record length. `Packed' *MySQL* strips spaces from the end of strings. The `Packed' value indicates the percentage savings achieved by doing this. `Recordspace used' What percentage of the data file is used. `Empty space' What percentage of the data file is unused. `Blocks/Record' Average number of blocks per record (i.e., how many links a fragmented record is composed of). This is always 1 for fixed-format tables. This value should stay as close to 1.0 as possible. If it gets too big, you can reorganize the table with `isamchk'. *Note Optimization::. `Recordblocks' How many blocks (links) are used. For fixed format, this is the same as the number of records. `Deleteblocks' How many blocks (links) are deleted. `Recorddata' How many bytes in the data file are used. `Deleted data' How many bytes in the data file are deleted (unused). `Lost space' If a record is updated to a shorter length, some space is lost. This is the sum of all such losses, in bytes. `Linkdata' When the dynamic table format is used, record fragments are linked with pointers (4 to 7 bytes each). `Linkdata' is the sum of the amount of storage used by all such pointers. If a table has been compressed with `pack_isam', `isamchk -d' prints additional information about each table column. See *Note `pack_isam': pack_isam, for an example of this information and a description of what it means. Using `isamchk' for crash recovery ================================== The file format that *MySQL* uses to store data has been extensively tested, but there are always external circumstances that may cause database tables to become corrupted: * The `mysqld' process being killed in the middle of a write * Unexpected shutdown of the computer (for example, if the computer is turned off) * A hardware error This chapter describes how to check for and deal with data corruption in *MySQL* databases. When performing crash recovery, it is important to understand that each table `tbl_name' in a database corresponds to three files in the database directory: *File* *Purpose* `tbl_name.frm' Table definition (form) file `tbl_name.ISD' Data file `tbl_name.ISM' Index file Each of these three file types is subject to corruption in various ways, but problems occur most often in data files and index files. `isamchk' works by creating a copy of the `.ISD' (data) file row by row. It ends the repair stage by removing the old `.ISD' file and renaming the new file to the original file name. If you use `--quick', `isamchk' does not create a temporary `.ISD' file, but instead assumes that the `.ISD' file is correct and only generates a new index file without touching the `.ISD' file. This is safe, because `isamchk' automatically detects if the `.ISD' file is corrupt and aborts the repair in this case. You can also give two `--quick' options to `isamchk'. In this case, `isamchk' does not abort on some errors (like duplicate key) but instead tries to resolve them by modifying the `.ISD' file. Normally the use of two `--quick' options is useful only if you have too little free disk space to perform a normal repair. In this case you should at least make a backup before running `isamchk'. How to check tables for errors ------------------------------ To check a table, use the following commands: `isamchk tbl_name' This finds 99.99% of all errors. What it can't find is corruption that involves *ONLY* the data file (which is very unusual). If you want to check a table, you should normally run `isamchk' without options or with either the `-s' or `--silent' option. `isamchk -e tbl_name' This does a complete and thorough check of all data (`-e' means "extended check"). It does a check-read of every key for each row to verify that they indeed point to the correct row. This may take a LONG time on a big table with many keys. `isamchk' will normally stop after the first error it finds. If you want to obtain more information, you can add the `--verbose' (`-v') option. This causes `isamchk' to keep going, up through a maximum of 20 errors. In normal usage, a simple `isamchk' (with no arguments other than the table name) is sufficient. `isamchk -e -i tbl_name' Like the previous command, but the `-i' option tells `isamchk' to print some informational statistics, too. How to repair tables -------------------- The symptoms of a corrupted table are usually that queries abort unexpectedly and that you observe errors such as these: * `tbl_name.frm' is locked against change * Can't find file `tbl_name.ISM' (Errcode: ###) * Got error ### from table handler (Error 135 is an exception in this case) * Unexpected end of file * Record file is crashed In these cases, you must repair your tables. `isamchk' can usually detect and fix most things that go wrong. The repair process involves up to four stages, described below. Before you begin, you should `cd' to the database directory and check the permissions of the table files. Make sure they are readable by the Unix user that `mysqld' runs as (and to you, since you need to access the files you are checking). If it turns out you need to modify files, they must also be writable by you. *Stage 1: Checking your tables* Run `isamchk *.ISM' or (`isamchk -e *.ISM' if you have more time). Use the `-s' (silent) option to suppress unnecessary information. You have to repair only those tables for which `isamchk' announces an error. For such tables, proceed to Stage 2. If you get weird errors when checking (such as `out of memory' errors), or if `isamchk' crashes, go to Stage 3. *Stage 2: Easy safe repair* First, try `isamchk -r -q tbl_name' (`-r -q' means "quick recovery mode"). This will attempt to repair the index file without touching the data file. If the data file contains everything that it should and the delete links point at the correct locations within the data file, this should work and the table is fixed. Start repairing the next table. Otherwise, use the following procedure: 1. Make a backup of the data file before continuing. 2. Use `isamchk -r tbl_name' (`-r' means "recovery mode"). This will remove incorrect records and deleted records from the data file and reconstruct the index file. 3. If the preceding step fails, use `isamchk --safe-recover tbl_name'. Safe recovery mode uses an old recovery method that handles a few cases that regular recovery mode doesn't (but is slower). If you get weird errors when repairing (such as `out of memory' errors), or if `isamchk' crashes, go to Stage 3. *Stage 3: Difficult repair* You should only reach this stage if the first 16K block in the index file is destroyed or contains incorrect information, or if the index file is missing. In this case, it's necessary to create a new index file. Do so as follows: 1. Move the data file to some safe place. 2. Use the table description file to create new (empty) data and index files: shell> mysql db_name mysql> DELETE FROM tbl_name; mysql> quit 3. Copy the old data file back onto the newly created data file. (Don't just move the old file back onto the new file; you want to retain a copy in case something goes wrong.) Go back to Stage 2. `isamchk -r -q' should work now. (This shouldn't be an endless loop). *Stage 4: Very difficult repair* You should reach this stage only if the description file has also crashed. That should never happen, because the description file isn't changed after the table is created. 1. Restore the description file from a backup and go back to Stage 3. You can also restore the index file and go back to Stage 2. In the latter case, you should start with `isamchk -r'. 2. If you don't have a backup but know exactly how the table was created, create a copy of the table in another database. Remove the new data file, then move the description and index files from the other database to your crashed database. This gives you new description and index files, but leaves the data file alone. Go back to Stage 2 and attempt to reconstruct the index file. Table optimization ------------------ To coalesce fragmented records and eliminate wasted space resulting from deleting or updating records, run `isamchk' in recovery mode: shell> isamchk -r tbl_name You can optimize a table in the same way using the SQL `OPTIMIZE TABLE' statement. `OPTIMIZE TABLE' is easier, but `isamchk' is faster. `isamchk' also has a number of other options you can use to improve the performance of a table: `-S, --sort-index' Sort the index tree blocks in high-low order. This will optimize seeks and will make table scanning by key faster. `-R index_num, --sort-records=index_num' Sorts records according to an index. This makes your data much more localized and may speed up ranged `SELECT' and `ORDER BY' operations on this index. (It may be VERY slow to do a sort the first time!) To find out a table's index numbers, use `SHOW INDEX', which shows a table's indexes in the same order that `isamchk' sees them. Indexes are numbered beginning with 1. `-a, --analyze' Analyzes the distribution of keys in a table. This improves join performance when you retrieve records from the table later. Adding new functions to *MySQL* ******************************* There are two ways to add new functions to *MySQL*: * You can add the function through the user-definable function (UDF) interface. User-definable functions are added and removed dynamically using the `CREATE FUNCTION' and `DROP FUNCTION' statements. *Note Create function::. * You can add the function as a native (built in) *MySQL* function. Native functions are compiled into the `mysqld' server and become available on a permanent basis. Each method has advantages and disadvantages: * If you write a user-definable function, you must install the object file in addition to the server itself. If you compile your function into the server, you don't need to do that. * You can add UDFs to a binary *MySQL* distribution. Native functions require you to modify a source distribution. * If you upgrade your *MySQL* distribution, you can continue to use your previously-installed UDFs. For native functions, you must repeat your modifications each time you upgrade. Whichever method you use to add new functions, they may be used just like native functions such as `ABS()' or `SOUNDEX()'. Adding a new user-definable function ==================================== For the UDF mechanism to work, functions must be written in C or C++ and your operating system must support dynamic loading. The *MySQL* source distribution includes a file `sql/udf_example.cc' that defines 5 new functions. Consult this file to see how UDF calling conventions work. For each function that you want to use in SQL statements, you should define corresponding C (or C++) functions. In the discussion below, the name "xxx" is used for an example function name. To distinquish between SQL and C/C++ usage, `XXX()' (uppercase) indicates a SQL function call, and `xxx()' (lowercase) indicates a C/C++ function call. The C/C++ functions that you write to implement the inferface for `XXX()' are: `xxx()' (required) The main function. This is where the function result is computed. The correspondence between the SQL type and return type of your C/C++ function is shown below: *SQL type* *C/C++ type* `STRING' `char *' `INTEGER' `long long' `REAL' `double' `xxx_init()' (optional) The initialization function for `xxx()'. It can be used to: * Check the number of arguments to `XXX()' * Check that the arguments are of a required type, or, alternatively, tell *MySQL* to coerce arguments to the types you want when the main function is called * Allocate any memory required by the main function * Specify the maximum length of the result * Specify (for `REAL' functions) the maximum number of decimals * Specify whether or not the result can be `NULL' `xxx_deinit()' (optional) The deinitialization function for `xxx()'. It should deallocate any memory allocated by the initialization function. When a SQL statement invokes `XXX()', *MySQL* calls the initialization function `xxx_init()' to let it perform any required setup, such as argument checking or memory allocation. If `xxx_init()' returns an error, the SQL statement is aborted with an error message and the main and deinitialization functions are not called. Otherwise, the main function `xxx()' is called once for each row. After all rows have been processed, the deinitialization function `xxx_deinit()' is called so it can perform any required cleanup. All functions must be thread-safe (not just the main function, but the initialization and deinitialization functions as well). This means that you are not allowed to allocate any global or static variables that change! If you need memory, you should allocate it in `xxx_init()' and free it in `xxx_deinit()'. UDF calling sequences --------------------- The main function should be declared as shown below. Note that the return type and parameters differ, depending on whether you will declare the SQL function `XXX()' to return `STRING', `INTEGER' or `REAL' in the `CREATE FUNCTION' statement: For `STRING' functions: char *xxx(UDF_INIT *initid, UDF_ARGS *args, char *result, unsigned long *length, char *is_null, char *error); For `INTEGER' functions: long long xxx(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error); For `REAL' functions: double xxx(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error); The initialization and deinitialization functions are declared like this: my_bool xxx_init(UDF_INIT *initid, UDF_ARGS *args, char *message); void xxx_deinit(UDF_INIT *initid); The `initid' parameter is passed to all three functions. It points to a `UDF_INIT' structure that is used to communicate information between functions. The `UDF_INIT' structure members are listed below. The initialization function should fill in any members that it wishes to change. (To use the default for a member, leave it unchanged.) `my_bool maybe_null' `xxx_init()' should set `maybe_null' to `1' if `xxx()' can return `NULL'. The default value is `1' if any of the arguments are declared `maybe_null'. `unsigned int decimals' Number of decimals. The default value is the maximum number of decimals in the arguments passed to the main function. (For example, if the function is passed `1.34', `1.345' and `1.3', the default would be 3, since `1.345' has 3 decimals. `unsigned int max_length' The maximum length of the string result. The default value differs depending on the result type of the function. For string functions, the default is the length of the longest argument. For integer functions, the default is 21 digits. For real functions, the default is 13 plus the number of decimals indicated by `initid->decimals'. (For numeric functions, the length includes any sign or decimal point characters.) `char *ptr' A pointer that the function can use for its own purposes. For example, functions can use `initid->ptr' to communicate allocated memory between functions. In `xxx_init()', allocate the memory and assign it to this pointer: initid->ptr = allocated_memory; In `xxx()' and `xxx_deinit()', refer to `initid->ptr' to use or deallocate the memory. Argument processing ------------------- The `args' parameter points to a `UDF_ARGS' structure which has the members listed below: `unsigned int arg_count' The number of arguments. Check this value in the initialization function if you want your function to be called with a particular number of arguments. For example: if (args->arg_count != 2) { strcpy(message,"XXX() requires two arguments"); return 1; } `enum Item_result *arg_type' The types for each argument. The possible type values are `STRING_RESULT', `INT_RESULT' and `REAL_RESULT'. To make sure that arguments are of a given type and return an error if they are not, check the `arg_type' array in the initialization function. For example: if (args->arg_type[0] != STRING_RESULT && args->arg_type[1] != INT_RESULT) { strcpy(message,"XXX() requires a string and an integer"); return 1; } As an alternative to requiring your function's arguments to be of particular types, you can use the initialization function to set the `arg_type' elements to the types you want. This causes *MySQL* to coerce arguments to those types for each call to `xxx()'. For example, to specify coercion of the first two arguments to string and integer, do this in `xxx_init()': args->arg_type[0] = STRING_RESULT; args->arg_type[1] = INT_RESULT; `char **args' `args->args' communicates information to the initialization function about the general nature of the arguments your function was called with. For a constant argument `i', `args->args[i]' points to the argument value. (See below for instructions on how to access the value properly.) For a non-constant argument, `args->args[i]' is `0'. A constant argument is an expression that uses only constants, such as `3' or `4*7-2' or `SIN(3.14)'. A non-constant argument is an expression that refers to values that may change from row to row, such as column names or functions that are called with non-constant arguments. For each invocation of the main function, `args->args' contains the actual arguments that are passed for the row currently being processed. Functions can refer to an argument `i' as follows: * An argument of type `STRING_RESULT' is given as a string pointer plus a length, to allow handling of binary data or data of arbitrary length. The string contents are available as `args->args[i]' and the string length is `args->lengths[i]'. You should not assume that strings are null-terminated. * For an argument of type `INT_RESULT', you must cast `args->args[i]' to a `long long' value: long long int_val; int_val = *((long long*) args->args[i]); * For an argument of type `REAL_RESULT', you must cast `args->args[i]' to a `double' value: double real_val; real_val = *((double*) args->args[i]); `unsigned long *lengths' For the initialization function, the `lengths' array indicates the maximum string length for each argument. For each invocation of the main function, `lengths' contains the actual lengths of any string arguments that are passed for the row currently being processed. For arguments of types `INT_RESULT' or `REAL_RESULT', `lengths' still contains the maximum length of the argument (as for the initialization function). Return values and error handling -------------------------------- The initialization function should return `0' if no error occurred and `1' otherwise. If an error occurs, `xxx_init()' should store a null-terminated error message in the `message' parameter. The message will be returned to the client. The message buffer is `MYSQL_ERRMSG_SIZE' characters long, but you should try to keep the message to less than 80 characters so that it fits the width of a standard terminal screen. The return value of the main function `xxx()' is the function value, for `long long' and `double' functions. For string functions, the string is returned in the `result' and `length' arguments. `result' is a buffer at least 255 bytes long. Set these to the contents and length of the return value. For example: memcpy(result, "result string", 13); *length = 13; The string function return value normally also points to the result. To indicate a return value of `NULL' in the main function, set `is_null' to `1': *is_null = 1; To indicate an error return in the main function, set the `error' parameter to `1': *error = 1; If `xxx()' sets `*error' to `1' for any row, the function value is `NULL' for the current row and for any subsequent rows processed by the statement in which `XXX()' was invoked. (`xxx()' will not even be called for subsequent rows.) *Note:* in *MySQL* versions prior to 3.22.10, you should set both `*error' and `*is_null': *error = 1; *is_null = 1; Compiling and installing user-definable functions ------------------------------------------------- Files implementing UDFs must be compiled and installed on the host where the server runs. This process is described below for the example UDF file `udf_example.cc' that is included in the *MySQL* source distribution. This file contains the following functions: * `metaphon()' returns a metaphon string of the string argument. This is something like a soundex string, but it's more tuned for English. * `myfunc_double()' returns the sum of the ASCII values of the characters in its arguments, divided by the sum of the length of its arguments. * `myfunc_int()' returns the sum of the length of its arguments. * `lookup()' returns the IP number for a hostname. * `reverse_lookup()' returns the hostname for an IP number. The function may be called with a string `"xxx.xxx.xxx.xxx"' or four numbers. A dynamically-loadable file should be compiled as a sharable object file, using a command something like this: shell> gcc -shared -o udf_example.so myfunc.cc You can easily find out the correct compiler options for your system by running this command in the `sql' directory of your *MySQL* source tree: shell> make udf_example.o You should run a compile command similar to the one that `make' displays, except that you should remove the `-c' option near the end of the line and add `-o udf_example.so' to the end of the line. (On some systems, you may need to leave the `-c' on the command.) Once you compile a shared object containing UDFs, you must install it and tell *MySQL* about it. Compiling a shared object from `udf_example.cc' produces a file named something like `udf_example.so' (the exact name may vary from platform to platform). Copy this file to some directory searched by `ld', such as `/usr/lib'. After the library is installed, notify `mysqld' about the new functions with these commands: mysql> CREATE FUNCTION metaphon RETURNS STRING SONAME "udf_example.so"; mysql> CREATE FUNCTION myfunc_double RETURNS REAL SONAME "udf_example.so"; mysql> CREATE FUNCTION myfunc_int RETURNS INTEGER SONAME "udf_example.so"; mysql> CREATE FUNCTION lookup RETURNS STRING SONAME "udf_example.so"; mysql> CREATE FUNCTION reverse_lookup RETURNS STRING SONAME "udf_example.so"; Functions can be deleted using `DROP FUNCTION': mysql> DROP FUNCTION metaphon; mysql> DROP FUNCTION myfunc_double; mysql> DROP FUNCTION myfunc_int; mysql> DROP FUNCTION lookup; mysql> DROP FUNCTION reverse_lookup; The `CREATE FUNCTION' and `DROP FUNCTION' statements update the system table `func' in the `mysql' database. The function's name, type and shared library name are saved in the table. You must have the *insert* and *delete* privileges for the `mysql' database to create and drop functions. You should not use `CREATE FUNCTION' to add a function that has already been created. If you need to reinstall a function, you should remove it with `DROP FUNCTION' and then reinstall it with `CREATE FUNCTION'. You would need to do this, for example, if you recompile a new version of your function, so that `mysqld' gets the new version. Otherwise the server will continue to use the old version. Active functions are reloaded each time the server starts, unless you start `mysqld' with the `--skip-grant-tables' option. In this case, UDF initialization is skipped and UDFs are unavailable. (An active function is one that has been loaded with `CREATE FUNCTION' and not removed with `DROP FUNCTION'.) Adding a new native function ============================ The procedure for adding a new native function is described below. Note that you cannot add native functions to a binary distribution since the procedure involves modifying *MySQL* source code. You must compile *MySQL* yourself from a source distribution. Also note that if you migrate to another version of *MySQL* (e.g., when a new version is released), you will need to repeat the procedure with the new version. To add a new native *MySQL* function, follow these steps: 1. Add one line to `lex.h' that defines the function name in the `sql_functions[]' array. 2. Add two lines to `sql_yacc.yy'. One indicates the preprocessor symbol that `yacc' should define (this should be added at the beginning of the file). Then define the function parameters and add an "item" with these parameters to the `simple_expr' parsing rule. For an example, check all occurrences of `SOUNDEX' in `sql_yacc.yy' to see how this is done. 3. In `item_func.h', declare a class inheriting from `Item_num_func' or `Item_str_func', depending on whether your function returns a number or a string. 4. In `item_func.cc', add one of the following declarations, depending on whether you are defining a numeric or string function: double Item_func_newname::val() longlong Item_func_newname::val_int() String *Item_func_newname::Str(String *str) 5. You should probably also define the following function: void Item_func_newname::fix_length_and_dec() This function should at least calculate `max_length' based on the given arguments. `max_length' is the maximum number of characters the function may return. This function should also set `maybe_null = 0' if the main function can't return a `NULL' value. The function can check if any of the function arguments can return `NULL' by checking the arguments `maybe_null' variable. All functions must be thread-safe. For string functions, there are some additional considerations to be aware of: * The `String *str' argument provides a string buffer that may be used to hold the result. * The function should return the string that holds the result. * All current string functions try to avoid allocating any memory unless absolutely necessary! *MySQL* ODBC Support ******************** *MySQL* provides support for ODBC by means of the *MyODBC* program. Operating systems supported by *MyODBC* ======================================= *MyODBC* is a 32-bit ODBC (2.50) level 0 driver for Windows95 and Windows NT. We hope somebody will port it to Windows 3.x. How to report problems with *MyODBC* ==================================== ODBC has been tested with Access, Admndemo.exe, C++-Builder, Centura Team Developer (formerly Gupta SQL/Windows), ColdFusion (on Solaris), Crystal Reports, Delphi, Excel, iHTML, FileMaker Pro, FoxPro, Notes 4.5/4.6, SBSS, perl DBD-ODBC, Paradox, Powerbuilder, VC++ and Visual Basic. If you know of any other application that works with *MyODBC*, please mail about this! If you encounter difficulties, we would like to have the log file from the ODBC manager (the log you get when requesting logs from ODBCADMIN) and a *MyODBC* log. This will help shed some light on any problems. To get a *MyODBC* log, please tag the 'Trace MyODBC' option flag in the *MyODBC* connect/configure screen. The log will be written to file `c:\myodbc.log'. Note that you must use `MYSQL.DLL' and not `MYSQL2.DLL' for this option to work! Programs known to work with *MyODBC* ==================================== Most programs should work with *MyODBC*, but for each of those listed below, we have tested it ourselves or gotten confirmation from some user that it works: *Program* *Comment* Access To make Access work: * You should have a primary key in the table. * You should have a timestamp in all tables you want to be able to update.. * Only use double float fields. Access fails when comparing with single floats. * Set the 'Return matching rows' option field when connecting to *MySQL*. * Access on NT will report `BLOB' columns as `OLE OBJECTS'. If you want to have `MEMO' columns instead, you should change the column to `TEXT' with `ALTER TABLE'. Excel Works. Some tips: * If you have problems with dates, try to select them as strings using the `CONCAT()' function. For example: select CONCAT(rise_time), CONCAT(set_time) from sunrise_sunset; Values retrieved as strings this way should be correctly recognized as time values by Excel97. The purpose of `CONCAT()' in this example is to fool ODBC into thinking the column is of "string type". Without the `CONCAT()', ODBC knows the column is of time type, and Excel does not understand that. Note that this is a bug in Excel, because it automatically converts a string to a time. This would be great if the source was a text file, but is plain stupid when the source is an ODBC connection that reports exact types for each column. odbcadmin Test program for ODBC. Delphi You must use DBE 3.2 or newer. Set the 'Don't optimize column width' option field when connecting to *MySQL*. Also, here is some potentially useful delphi code that sets up both an ODBC entry and a BDE entry for MyODBC (the BDE entry requires a BDE Alias Editor which may be had for free at a Delphi Super Page near you.): (Thanks to Bryan Brunton for this) fReg:= TRegistry.Create; fReg.OpenKey('\Software\ODBC\ODBC.INI\DocumentsFab', True); fReg.WriteString('Database', 'Documents'); fReg.WriteString('Description', ' '); fReg.WriteString('Driver', 'C:\WINNT\System32\myodbc.dll'); fReg.WriteString('Flag', '1'); fReg.WriteString('Password', ''); fReg.WriteString('Port', ' '); fReg.WriteString('Server', 'xmark'); fReg.WriteString('User', 'winuser'); fReg.OpenKey('\Software\ODBC\ODBC.INI\ODBC Data Sources', True); fReg.WriteString('DocumentsFab', 'MySQL'); fReg.CloseKey; fReg.Free; Memo1.Lines.Add('DATABASE NAME='); Memo1.Lines.Add('USER NAME='); Memo1.Lines.Add('ODBC DSN=DocumentsFab'); Memo1.Lines.Add('OPEN MODE=READ/WRITE'); Memo1.Lines.Add('BATCH COUNT=200'); Memo1.Lines.Add('LANGDRIVER='); Memo1.Lines.Add('MAX ROWS=-1'); Memo1.Lines.Add('SCHEMA CACHE DIR='); Memo1.Lines.Add('SCHEMA CACHE SIZE=8'); Memo1.Lines.Add('SCHEMA CACHE TIME=-1'); Memo1.Lines.Add('SQLPASSTHRU MODE=SHARED AUTOCOMMIT'); Memo1.Lines.Add('SQLQRYMODE='); Memo1.Lines.Add('ENABLE SCHEMA CACHE=FALSE'); Memo1.Lines.Add('ENABLE BCD=FALSE'); Memo1.Lines.Add('ROWSET SIZE=20'); Memo1.Lines.Add('BLOBS TO CACHE=64'); Memo1.Lines.Add('BLOB SIZE=32'); AliasEditor.Add('DocumentsFab','MySQL',Memo1.Lines); C++Builder Tested with BDE 3.0. The only known problem is that when the table schema changes, query fields are not updated. BDE however does not seem to recognize primary keys, only the index PRIMARY, though this has not been a problem. How to fill in the various fields in the ODBC administrator program =================================================================== There are three possibilities for specifying the server name on Windows95: * Use the IP address of the server. * Add a file `lmhosts' with the following info: ip hostname For example: 194.216.84.21 my * Configure the PC to use DNS. Example of how to fill in the "ODBC setup": Windows DSN name: test Description: This is my test database MySql Database: test Server: 194.216.84.21 User: monty Password: my_password Port: The value for the `Windows DSN name' field is any name that is unique in your windows ODBC setup. You don't have to specify values for the `Server', `User', `Password' or `Port' fields in the ODBC setup screen. However, if you do, the values will be used as the defaults later when you attempt to make a connection. You have the option of changing the values at that time. If the port number is not given, the default port (3306) is used. How to get the value of an `AUTO_INCREMENT' column in ODBC ========================================================== A common problem is how to get the value of an automatically-generated ID from an `INSERT'. With ODBC, you can do something like this (assuming that `auto' is an `AUTO_INCREMENT' field): INSERT INTO foo (auto,text) VALUES(NULL,'text'); SELECT LAST_INSERT_ID(); Or, if you are just going to insert the ID into another table, you can do this: INSERT INTO foo (auto,text) VALUES(NULL,'text'); INSERT INTO foo2 (id,text) VALUES(LAST_INSERT_ID(),'text'); For the benefit of some ODBC applications (at least Delphi and Access), the following query can be used to find a newly-inserted row: SELECT * FROM tbl_name WHERE auto IS NULL; Problems and common errors ************************** Some common errors when using *MySQL* ===================================== `MySQL server has gone away' error ---------------------------------- The most common reason for the `MySQL server has gone away' error is that the server timed out and closed the connection. By default, the server closes the connection after 8 hours if nothing has happened. You can check that the *MySQL* hasn't died by executing `mysqladmin version' and examining the uptime. If you have a script, you just have to issue the query again for the client to do an automatic reconnection. You normally can get the following error codes in this case (which one you get is OS-dependent): `CR_SERVER_GONE_ERROR' The client couldn't send a question to the server. `CR_SERVER_LOST' The client didn't get an error when writing to the server, but it didn't get a full answer (or any answer) to the question. You can also get these errors if you send a query to the server that is incorrect or too large. If `mysqld' gets a packet that is too large or out of order, it assumes that something has gone wrong with the client and closes the connection. If you need big queries (for example, if you are working with big `BLOB' columns), you can increase the query limit by starting `mysqld' with the `-O max_allowed_packet=#' option (default 1M). The extra memory is allocated on demand, so `mysqld' will use more memory only when you issue a big query or when `mysqld' must return a big result row! `Can't connect to local MySQL server' error ------------------------------------------- A *MySQL* client can connect to the `mysqld' server in two different ways: Unix sockets, which connect through a file in the file system (default `/tmp/mysqld.sock'), or TCP/IP, which connects through a port number. Unix sockets are faster than TCP/IP but can only be used when connecting to a server on the same computer. Unix sockets are used if you don't specify a hostname or if you specify the special hostname `localhost'. Here are some reasons the `Can't connect to local MySQL server' error might occur: * `mysqld' is not running. Check (using `ps') that there is a process running named `mysqld'. If there is, you can check the server by trying these different connections (the port number and socket pathname might be different in your setup, of course): shell> mysqladmin version shell> mysqladmin -h `hostname` version shell> mysqladmin -h `hostname` --port=3306 version shell> mysqladmin --socket=/tmp/mysql.sock version Note the use of backquotes rather than forward quotes with the `hostname' command; these cause the output of `hostname' (i.e., the current hostname) to be substituted into the `mysqladmin' command. * You are running on a system that uses MIT-pthreads. If you are running on a system that doesn't have native threads, `mysqld' uses the MIT-pthreads package. *Note Which OS::. However, MIT-pthreads doesn't support Unix sockets, so on such a system you must always specify the hostname explicitly when connecting to the server. Try using this command to check the connection to the server: shell> mysqladmin -h `hostname` version * Someone has removed the Unix socket that `mysqld' uses (default `/tmp/mysqld.sock'). You might have a `cron' job that removes the *MySQL* socket (e.g., a job that removes old files from the `/tmp' directory). You can always run `mysqladmin version' and check that the socket `mysqladmin' is trying to use really exists. The fix in this case is to change the `cron' job to not remove `mysqld.sock' or to place the socket somewhere else. You can specify a different socket location at *MySQL* configuration time with this command: shell> ./configure --with-unix-socket-path=/path/to/socket You can also start `safe_mysqld' with the `--socket=/path/to/socket' option and set the environment variable `MYSQL_UNIX_PORT' to the socket pathname before starting your *MySQL* clients. * You have started the `mysqld' server with the `--socket=/path/to/socket' option. If you change the socket pathname for the server, you must also notify the *MySQL* clients about the new path. You can do this by setting the environment variable `MYSQL_UNIX_PORT' to the socket pathname or by providing the socket path as an argument to the clients. You can test the socket with this command: shell> mysqladmin --socket=/path/to/socket version `Host '...' is blocked' error ----------------------------- If you get a error like this: Host 'hostname' is blocked because of many connection errors. Unblock with 'mysqladmin flush-hosts' This means that `mysqld' has gotten a lot (`max_connect_errors') of connect requests from the host `'hostname'' that have been interrupted in the middle. After `max_connect_errors' failed requests, `mysqld' assumes that something is wrong (like a attack from a cracker), and blocks the site from further connections until someone executes the command `mysqladmin flush-hosts'. By default, `mysqld' blocks a host after 10 connection errors. You can easily adjust this by starting the server like this: shell> safe_mysqld -O max_connect_errors=10000 & Note that if you get this error message for a given host, you should first check that there isn't anything wrong with TCP/IP connections from that host. If your TCP/IP connections aren't working, it won't do you any good to increase the value of the `max_connect_errors' variable! `Out of memory' error --------------------- If you issue a query and get something like the following error: mysql: Out of memory at line 42, 'malloc.c' mysql: needed 8136 byte (8k), memory in use: 12481367 bytes (12189k) ERROR 2008: MySQL client ran out of memory Note that the error refers to the *MySQL* client `mysql'. The reason for this error is simply that the client does not have enough memory to store the whole result. To remedy the problem, first check that your query is correct. Is it reasonable that it should return so many rows? If so, you can use `mysql --quick', which uses `mysql_use_result()' to retrieve the result set. This places less of a load on the client (but more on the server). `Packet too large' error ------------------------ When a *MySQL* client or the `mysqld' server gets a packet bigger than `max_allowed_packet' bytes, it issues a `Packet too large' error and closes the connection. If you are using the `mysql' client, you may specify a bigger buffer by starting the client with `mysql --set-variable=max_allowed_packet=8M'. If you are using other clients that do not allow you to specify the maximum packet size (such as `DBI'), you need to set the packet size when you start the server. You cau use a command-line option to `mysqld' to set `max_allowed_packet' to a larger size. For example, if you are expecting to store the full length of a `BLOB' into a table, you'll need to start the server with the `--set-variable=max_allowed_packet=24M' option. `The table is full' error ------------------------- This error occurs when an in-memory temporary table becomes larger than `tmp_table_size' bytes. To avoid this problem, you can use the `-O tmp_table_size=#' option to `mysqld' to increase the temporary table size, or use the SQL option `SQL_BIG_TABLES' before you issue the problematic query. *Note Set option::. You can also start `mysqld' with the `--big-tables' option. This is exactly the same as using `SQL_BIG_TABLES' for all queries. `Commands out of sync' error in client -------------------------------------- If you get `Commands out of sync; You can't run this command now' in your client code, you are calling client functions in the wrong order! This can happen, for example, if you are using `mysql_use_result()' and try to execute a new query before you have called `mysql_free_result()'. It can also happen if you try to execute two queries that return data without a `mysql_use_result()' or `mysql_store_result()' in between. `Ignoring user' error --------------------- If you get the following error: `Found wrong password for user: 'some_user@some_host'; Ignoring user' This means that when `mysqld' was started or when it reloaded the permissions tables, it found an entry in the `user' table with an invalid password. As a result, the entry is simply ignored by the permission system. Possible causes of and fixes for this problem: * You may be running a new version of `mysqld' with an old `user' table. You can check this by executing `mysqlshow mysql user' to see if the password field is shorter than 16 characters. If so, you can correct this condition by running the `scripts/add_long_password' script. * The user has an old password (8 chararacters long) and you didn't start `mysqld' with the `--old-protocol' option. Update the user in the `user' table with a new password or restart `mysqld' with `--old-protocol'. * You have specified a password in the `user' table without using the `PASSWORD()' function. Use `mysql' to update the user in the `user' table with a new password. Make sure to use the `PASSWORD()' function: mysql> update user set password=PASSWORD('your password') where user='XXX'; `Table 'xxx' doesn't exist' error --------------------------------- If you get the error `Table 'xxx' doesn't exist' or `Can't find file: 'xxx' (errno: 2)', this means that no table exists in the current database with the name `xxx'. Note that as *MySQL* uses directories and files to store databases and tables, the database and table names are *case sensitive*! (On Win32 the databases and tables names are not case sensitive, but all references to a given table within a query must use the same case!) You can check which tables you have in the current database with `SHOW TABLES'. *Note Show::. How *MySQL* handles a full disk =============================== When a disk full condition occurs, *MySQL* does the following: * It checks once every minute to see whether or not there is enough space to write the current row. If there is enough space, it continues as if nothing had happened. * Every 6 minutes it writes an entry to the log file warning about the disk full condition. To alleviate the problem, you can take the following actions: * To continue, you only have to free enough disk space to insert all records. * To abort the thread, you must send a `mysqladmin kill' to the thread. The thread will be aborted the next time it checks the disk (in 1 minute). * Note that other threads may be waiting for the table that caused the "disk full" condition. If you have several "locked" threads, killing the one thread that is waiting on the disk full condition will allow the other threads to continue. How to run SQL commands from a text file ======================================== The `mysql' client typically is used interactively, like this: shell> mysql database However, it's also possible to put your SQL commands in a file and tell `mysql' to read its input from that file. To do so, create a text file `text_file' that contains the commands you wish to execute. Then invoke `mysql' as shown below: shell> mysql database < text_file You can also start your text file with a `USE db_name' statement. In this case, it is unnecessary to specify the database name on the command line: shell> mysql < text_file *Note Programs::. Where *MySQL* stores temporary files ==================================== *MySQL* uses the value of the `TMPDIR' environment variable as the pathname of the directory in which to store temporary files. If you don't have `TMPDIR' set, *MySQL* uses the system default, which is normally `/tmp' or `/usr/tmp'. If the file system containing your temporary file directory is too small, you should edit `safe_mysqld' to set `TMPDIR' to point to a directory in a file system where you have enough space! You can also set the temporary directory using the `--tmpdir' option to `mysqld'. *MySQL* creates all temporary files as "hidden files". This ensures that the temporary files will be removed if `mysqld' is terminated. The disadvantage of using hidden files is that you will not see a big temporary file that fills up the file system in which the temporary file directory is located. When sorting (`ORDER BY' or `GROUP BY'), *MySQL* normally uses one or two temporary files. The maximum disk-space needed is: (length of what is sorted + sizeof(database pointer)) * number of matched rows * 2 `sizeof(database pointer)' is usually 4, but may grow in the future for really big tables. For some `SELECT' queries, *MySQL* also creates temporary SQL tables. These are not hidden and have names of the form `SQL_*'. `ALTER TABLE' creates a temporary table in the same directory as the original table. How to protect `/tmp/mysql.sock' from being deleted =================================================== If you have problems with the fact that anyone can delete the *MySQL* communication socket `/tmp/mysql.sock', you can, on most versions of Unix, protect your `/tmp' file system by setting the `sticky' bit on it. Log in as `root' and do the following: shell> chmod +s /tmp This will protect your `/tmp' file system so that files can be deleted only by their owners or the superuser (`root'). You can check if the `sticky' bit is set by executing `ls -ld /tmp'. If the last permission bit is `t', the bit is set. `Access denied' error ===================== *Note Privileges::. And especially see *Note Access denied::. How to run *MySQL* as a normal user =================================== The *MySQL* server `mysqld' can be started and run by any user. In order to change `mysqld' to run as Unix user `user_name', you must do the following: 1. Stop the server if it's running (use `mysqladmin shutdown'). 2. Change the database directories and files so that `user_name' has privileges to read and write files in them (you may need to do this as the Unix `root' user): shell> chown -R user_name /path/to/mysql/datadir If directories or files within the *MySQL* data directory are symlinks, you'll also need to follow those links and change the directories and files they point to. `chown -R' may not follow symlinks for you. 3. Start the server as user `user_name', or, if you are using *MySQL* 3.22 or later, start `mysqld' as the Unix `root' user and use the `--user=user_name' option. `mysqld' will switch to run as Unix user `user_name' before accepting any connections. 4. If you are using the `mysql.server' script to start `mysqld' when the system is rebooted, you should edit `mysql.server' to use `su' to run `mysqld' as user `user_name', or to invoke `mysqld' with the `--user' option. (No changes to `safe_mysqld' are necessary.) At this point, your `mysqld' process should be running fine and dandy as the Unix user `user_name'. One thing hasn't changed, though: the contents of the permissions tables. By default (right after running the permissions table install script `mysql_install_db'), the *MySQL* user `root' is the only user with permission to access the `mysql' database or to create or drop databases. Unless you have changed those permissions, they still hold. This shouldn't stop you from accessing *MySQL* as the *MySQL* `root' user when you're logged in as a Unix user other than `root'; just specify the `-u root' option to the client program. Note that accessing *MySQL* as `root', by supplying `-u root' on the command line, has *nothing* to do with *MySQL* running as the Unix `root' user, or, indeed, as other Unix user. The access permissions and user names of *MySQL* are completely separate from Unix user names. The only connection with Unix user names is that if you don't provide a `-u' option when you invoke a client program, the client will try to connect using your Unix login name as your *MySQL* user name. If your Unix box itself isn't secured, you should probably at least put a password on the *MySQL* `root' users in the access tables. Otherwise, any user with an account on that machine can run `mysql -u root db_name' and do whatever he likes. Problems with file permissions ============================== If you have problems with file permissions, for example, if `mysql' issues the following error message when you create a table: ERROR: Can't find file: 'path/with/filename.frm' (Errcode: 13) Then the environment variable `UMASK' might be set incorrectly when `mysqld' starts up. The default umask value is `0660'. You can change this behavior by starting `safe_mysqld' as follows: shell> UMASK=384 # = 600 in octal shell> export UMASK shell> /path/to/safe_mysqld & File not found ============== If you get `ERROR '...' not found (errno: 23)', `Can't open file: ... (errno: 24)' or any other error with `errno 23' or `errno 24' from *MySQL*, it means that you haven't allocated enough file descriptors for *MySQL*. You can use the `perror' utility to get a description of what the error number means: shell> perror 23 File table overflow shell> perror 24 Too many open files The problem here is that `mysqld' is trying to keep open too many files simultaneously. You can either tell `mysqld' not to open so many files at once, or increase the number of file descriptors available to `mysqld'. To tell `mysqld' to keep open fewer files at a time, you can make the table cache smaller by using the `-O table_cache=32' option to `safe_mysqld' (the default value is 64). Reducing the value of `max_connections' will also reduce the number of open files (the default value is 90). To change the number of file descriptors available to `mysqld', modify the `safe_mysqld' script. There is a commented-out line `ulimit -n 256' in the script. You can remove the `'#'' character to uncomment this line, and change the number 256 to change the number of file descriptors available to `mysqld'. `ulimit' can increase the number of file descriptors, but only up to the limit imposed by the operating system. If you need to increase the OS limit on the number of file descriptors available to each process, consult the documentation for your operating system. Problems using `DATE' columns ============================= The format of a `DATE' value is `'YYYY-MM-DD''. According to ANSI SQL, no other format is allowed. You should use this format in `UPDATE' expressions and in the WHERE clause of `SELECT' statements. For example: mysql> SELECT * FROM tbl_name WHERE date >= '1997-05-05'; As a convenience, *MySQL* automatically converts a date to a number if the date is used in a numeric context (and vice versa). It is also smart enough to allow a "relaxed" string form when updating and in a `WHERE' clause that compares a date to a `TIMESTAMP', `DATE' or a `DATETIME' column. (Relaxed form means that any non-numeric character may be used as the separator between parts. For example, `'1998-08-15'' and `'1998#08#15'' are equivalent.) *MySQL* can also convert a string containing no separators (such as `'19980815''), provided it makes sense as a date. The special date `'0000-00-00'' can be stored and retrieved as `'0000-00-00'.' When using a `'0000-00-00'' date through *MyODBC*, it will automatically be converted to `NULL' in *MyODBC* 2.50.12 and above, because ODBC can't handle this kind of date. Since *MySQL* performs the conversions described above, the following statements work: mysql> INSERT INTO tbl_name (idate) VALUES (19970505); mysql> INSERT INTO tbl_name (idate) VALUES ('19970505'); mysql> INSERT INTO tbl_name (idate) VALUES ('97-05-05'); mysql> INSERT INTO tbl_name (idate) VALUES ('1997.05.05'); mysql> INSERT INTO tbl_name (idate) VALUES ('1997 05 05'); mysql> INSERT INTO tbl_name (idate) VALUES ('0000-00-00'); mysql> SELECT idate FROM tbl_name WHERE idate >= '1997-05-05'; mysql> SELECT idate FROM tbl_name WHERE idate >= 19970505; mysql> SELECT mod(idate,100) FROM tbl_name WHERE idate >= 19970505; mysql> SELECT idate FROM tbl_name WHERE idate >= '19970505'; However, the following will not work: mysql> SELECT idate FROM tbl_name WHERE STRCMP(idate,'19970505')=0; `STRCMP()' is a string function, so it converts `idate' to a string and performs a string comparison. It does not convert `'19970505'' to a date and perform a date comparison. Note that *MySQL* does no checking whether or not the date is correct. If you store an incorrect date, such as `'1998-2-31'', the wrong date will be stored. If the date cannot be converted to any reasonable value, a `0' is stored in the `DATE' field. This is mainly a speed issue and we think it is up to the application to check the dates, and not the server. Case sensitivity in searches ============================ By default, *MySQL* searches are case-insensitive (although there are some character sets that are never case insensitive, such as `czech'). That means that if you search with `col_name LIKE 'a%'', you will get all column values that start with `A' or `a'. If you want to make this search case-sensitive, use something like `INDEX(col_name, "A")=0' to check a prefix. Or use `STRCMP(col_name, "A") = 0' if the column value must be exactly `"A"'. Simple comparison operations (`>=, >, = , < , <=', sorting and grouping) are based on each character's "sort value". Characters with the same sort value (like E, e and 'e) are treated as the same character! `LIKE' comparisons are done on the uppercase value of each character (E == e but E <> 'e) If you want a column always to be treated in case-sensitive fashion, declare it as `BINARY'. *Note Create table::. If you are using Chinese data in the so-called big5 encoding, you want to make all character columns `BINARY'. This works because the sorting order of big5 encoding characters is based on the order of ASCII codes. Problems with `NULL' values =========================== The concept of the `NULL' value is a common source of confusion for newcomers to SQL, who often think that `NULL' is the same thing as an empty string `'''. This is not the case! For example, the following statements are completely different: mysql> INSERT INTO my_table (phone) VALUES (NULL); mysql> INSERT INTO my_table (phone) VALUES (""); Both statements insert a value into the `phone' column, but the first inserts a `NULL' value and the second inserts an empty string. The meaning of the first can be regarded as "phone number is not known" and the meaning of the second can be regarded as "she has no phone". In SQL, the `NULL' value is always false in comparison to any other value, even `NULL'. An expression that contains `NULL' always produces a `NULL' value unless otherwise indicated in the documentation for the operators and functions involved in the expression. All columns in the following example return `NULL': mysql> SELECT NULL,1+NULL,CONCAT('Invisible',NULL); If you want to search for column values that are `NULL', you cannot use the `=NULL' test. The following statement returns no rows, because `expr = NULL' is FALSE, for any expression: mysql> SELECT * FROM my_table WHERE phone = NULL; To look for `NULL' values, you must use the `IS NULL' test. The following shows how to find the `NULL' phone number and the empty phone number: mysql> SELECT * FROM my_table WHERE phone IS NULL; mysql> SELECT * FROM my_table WHERE phone = ""; In *MySQL*, as in many other SQL servers, you can't index columns that can have `NULL' values. You must declare such columns `NOT NULL'. Conversely, you cannot insert `NULL' into an indexed column. When reading data with `LOAD DATA INFILE', empty columns are updated with `'''. If you want a `NULL' value in a column, you should use `\N' in the text file. The literal word `'NULL'' may also be used under some circumstances. *Note Load::. When using `ORDER BY', `NULL' values are presented first. If you sort in descending order using `DESC', `NULL' values are presented last. When using `GROUP BY', all `NULL' values are regarded as equal. To help with `NULL' handling, you can use the functions `IS NULL', `IS NOT NULL' and `IFNULL()'. For some column types, `NULL' values are handled specially. If you insert `NULL' into the first `TIMESTAMP' column of a table, the current time is inserted. If you insert `NULL' into an `AUTO_INCREMENT' column, the next number in the sequence is inserted. Problems with `alias' ===================== You can use alias to refer to a column in the `GROUP BY', `ORDER BY' or in the `HAVING' part. Aliases can also be used to give columns more better names: SELECT SQRT(a*b) as rt FROM table_name GROUP BY rt HAVING rt > 0; SELECT id,COUNT(*) AS cnt FROM table_name GROUP BY id HAVING cnt > 0; SELECT id AS "Customer identity" FROM table_name; Note that you ANSI SQL doesn't allow you to refer to an alias in a `WHERE' clause. This is because that when the `WHERE' code is executed the column value may not yet be determinated. For example the following query is *illegal*: SELECT id,COUNT(*) AS cnt FROM table_name WHERE cnt > 0 GROUP BY id; The `WHERE' statement is executed to determinate which rows should be included in the `GROUP BY' part while `HAVING' is used to decide which rows from the result set should be used. Deleting rows from related tables ================================= As *MySQL* doesn't support sub-selects or use of more than one table in the `DELETE' statement, you should use the following approach to delete rows from 2 related tables: 1. `SELECT' the rows based on some `WHERE' condition in the main table. 2. `DELETE' the rows in the main table based on the same condition. 3. `DELETE FROM related_table WHERE related_column IN (selected_rows)' If the total number of characters in the query with `related_column' is more than 1,048,576 (the default value of `max_allowed_packet', you should split it into smaller parts and execute multiple `DELETE' statements. You will probably get the fastest `DELETE' by only deleting 100-1000 `related_column' id's per time if the `related_column' is an index. If the `related_column' isn't an index, the speed is independent of the number of arguments in the `IN' clause. Solving problems with no matching rows ====================================== If you have a complicated query with many tables that doesn't return any rows, you should use the following procedure to find out what is wrong with your query: 1. Test the query with `EXPLAIN' and check if you can find something that is obviously wrong. *Note Explain::. 2. Select only those fields that are used in the `WHERE' clause. 3. Remove one table at a time from the query until it returns some rows. If the tables are big, it's a good idea to use `LIMIT 10' with the query. 4. Do a `SELECT' for the column that should have matched a row, against the table that was last removed from the query. 5. If you are comparing float or double with numbers that have decimals, you can't use `=' ! This problem is common in most computer languages as floating point values are not exact values. SELECT * FROM table_name WHERE float_column=3.5; -> SELECT * FROM table_name WHERE float_column between 3.45 and 3.55; 6. If you still can't find out what's wrong, create a minimal test that can be run with `mysql test < query.sql' that shows your problems. You can create a test file with `mysqldump --quick database tables > query.sql'. Take the file up in a editor, remove some insert lines (if there are too many of these) and add your select statement last in the file. Test that you still have your problem by doing: shell> mysqladmin create test2 shell> mysql test2 < query.sql Post the test file using `mysqlbug' to . Problems with `ALTER TABLE'. ============================ If `ALTER TABLE' dies with an error like this: Error on rename of './database/name.frm' to './database/B-a.frm' (Errcode: 17) The problem may be that *MySQL* has crashed in a previous `ALTER TABLE' and there is an old table named `A-something' or `B-something' lying around. In this case, go to the *MySQL* data directory and delete all files that have names starting with `A-' or `B-'. (You may want to move them elsewhere instead of deleting them). `ALTER TABLE' works the following way: * Create a new table named `A-xxx' with the requested changes. * All rows from the old table are copied to `A-xxx'. * The old table is renamed `B-xxx'. * `A-xxx' is renamed to your old table name. * `B-xxx' is deleted. If something goes wrong with the renaming operation, *MySQL* tries to undo the changes. If something goes seriously wrong (this shouldn't happen, of course), *MySQL* may leave the old table as `B-xxx' but a simple rename should get your data back. Solving some common problems with *MySQL* ***************************************** Database replication ==================== The most general way to replicate a database is to use the update log. *Note Update log::. This requires one database that acts as a master (to which data changes are made) and one or more other databases that act as slaves. To update a slave, just run `mysql < update_log'. Supply host, user and password options that are appropriate for the slave database, and use the update log from the master database as input. If you never delete anything from a table, you can use a `TIMESTAMP' column to find out which rows have been inserted or changed in the table since the last replication (by comparing to the time when you did the replication last time) and only copy these rows to the mirror. It is possible to make a two-way updating system using both the update log (for deletes) and timestamps (on both sides). But in that case you must be able to handle conflicts when the same data have been changed in both ends. You probably want to keep the old version to help with deciding what has been updated. Because replication in this case is done with SQL statements, you should not use the following functions in statements that update the database; they may not return the same value as in the original database: * `DATABASE()' * `GET_LOCK()' and `RELEASE_LOCK()' * `RAND()' * `USER()', `SYSTEM_USER()' or `SESSION_USER()' * `VERSION()' All time functions are safe to use, as the timestamp is sent to the mirror if needed. `LAST_INSERT_ID()' is also safe to use. Database backups ================ Since *MySQL* tables are stored as files, it is easy to do a backup. To get a consistent backup, do a `LOCK TABLES' on the relevant tables. *Note Lock tables::. You only need a read lock; this allows other threads to continue to query the tables while you are making a copy of the files in the database directory. If you want to make a SQL level backup, you can use `SELECT INTO OUTFILE'. Another way to backup a database is to use the `mysqldump' program: 1. Do a full backup of your databases: shell> mysqldump --tab=/path/to/some/dir --lock-tables --quick You can also simply copy all table files (`*.frm', `*.ISD' and `*.ISM' files), as long as the server isn't updating anything. 2. Stop `mysqld' if it's running, then start it with the `--log-update' option. You will get log files with names of the form `hostname.n', where `n' is a number that is incremented each time you execute `mysqladmin refresh' or `mysqladmin flush-logs', the `FLUSH LOGS' statement, or restart the server. These log files provide you with the information you need to replicate changes to the database that are made subsequent to the point at which you executed `mysqldump'. If you have to restore something, try to recover your tables using `isamchk -r' first. That should work in 99.9% of all cases. If `isamchk' fails, try the the following procedure: 1. Restore the original `mysqldump' backup. 2. Execute the following command to re-run the updates in the update logs: shell> ls -1 -t -r hostname.[0-9]* | xargs cat | mysql `ls' is used to get all the log files in the right order. You can also do selective backups with `SELECT * INTO OUTFILE 'file_name' FROM tbl_name' and restore with `LOAD DATA INFILE 'file_name' REPLACE ...' To avoid duplicate records, you need a `PRIMARY KEY' or a `UNIQUE' key in the table. The `REPLACE' keyword causes old records to be replaced with new ones when a new record duplicates an old record on a unique key value. Running multiple *MySQL* servers on the same machine ==================================================== There are circumstances when you might want to run multiple servers on the same machine. For example, you might want to test a new *MySQL* release while leaving your existing production setup undisturbed. Or you might be an Internet service provider that wants to provide independent *MySQL* installations for different customers. If you want to run multiple servers, the easiest way is to compile the servers with different TCP/IP ports and socket files so they are not both listening to the same TCP/IP port or socket file. Assume an existing server is configured for the default port number and socket file. Then configure the new server with a `configure' command something like this: shell> ./configure --with-tcp-port=port_number \ --with-unix-socket=file_name \ --prefix=/usr/local/mysql-3.22.9 Here `port_number' and `file_name' should be different than the default port number and socket file pathname, and the `--prefix' value should specify an installation directory different than the one under which the existing *MySQL* installation is located. You can check the socket and port used by any currently-executing *MySQL* server with this command: shell> mysqladmin -h hostname --port port_number variables If you have a *MySQL* server running on the port you used, you will get a list of some of the most important configurable variables in *MySQL*, including the socket name. You should also edit the initialization script for your machine (probably `mysql.server') to start and kill multiple `mysqld' servers. You don't have to recompile a new *MySQL* server just to start with a different port and socket. You can change the port and socket to be used by specifying them at runtime as options to `safe_mysqld': shell> /path/to/safe_mysqld --socket=file-name --port=file-name If you run the new server on the same database directory as another server with logging enabled, you should also specify the name of the log files to `safe_mysqld' with `--log' and `--log-update'. Otherwise, both servers may be trying to write to the same log file. *Warning*: Normally you should never have two servers that update data in the same database! If your OS doesn't support fault-free system locking, this may lead to unpleasant surprises! If you want to use another database directory for the second server, you can use the `--datadir=path' option to `safe_mysqld'. When you want to connect to a *MySQL* server that is running with a different port than the port that is compiled into your client, you can use one of the following methods: * Start the client with `--host 'hostname' --port=port-numer' or `[--host localhost] --socket=file-name'. * In your C or Perl programs, you can give the port and socket arguments when connecting to the *MySQL* server. * Set the `MYSQL_UNIX_PORT' and `MYSQL_TCP_PORT' environment variables to point to the Unix socket and TCP/IP port before you start your clients. If you normally use a specific socket or port, you should place commands to set these environment variables in your `.login' file. *Note Programs::. * Specify the default socket and TCP/IP port in the `.my.cnf' file in your home directory. *Note Option files::. *MySQL* client tools and API's ****************************** *MySQL* C API ============= The C API code is distributed with *MySQL*. It is included in the `mysqlclient' library and allows C programs to access a database. Many of the clients in the MySQL source distribution are written in C. If you are looking for examples showing how to use the C API, take a look at these clients. Most of the other client APIs (all except Java) use this library to connect. So, for example, you can use the same environment variables as the ones used by other client programs. *Note Programs::. The client has a maximum communication buffer size. The size of the buffer that is allocated initially (8192 bytes) is automatically increased up to the maximum size (the default for this is 24M). Since buffers are increased on demand (but not decreased until close), simply increasing the default limit doesn't cause more resources to be used. This size check is mostly a check for erroneous queries and communication packets. The communication buffer must be big enough to contain a single SQL statement and one row of returned data (not at the same time, of course). Each thread's communication buffer is dynamically enlarged to handle any row or query up to the imposed limit. For example, if you have `BLOB' values that contain up to 16M of data, you must have at least 16M as your communication buffer limit (in both server and client). *Note *MySQL* parameters: MySQL parameters. The *MySQL* server shrinks each communication buffer to `net_buffer_length' bytes after each query. The client doesn't shrink the buffer automatically; Client memory is reclaimed when the connection is closed. C API datatypes =============== `MYSQL' This structure represents a handle to one database connection. It is used for almost all *MySQL* functions. `MYSQL_RES' This structure represents the result of a query that returns rows (`SELECT' or `SHOW'). The information returned from a query is called the *result set* in the remainder of this section. `MYSQL_ROW' This is a type-safe representation of one row of data. It is currently implemented as an array of byte strings. `MYSQL_FIELD' This structure contains information about a field, such as the field's name, type and size. Its members are described in more detail below. You may obtain the `MYSQL_FIELD' structures for each field by calling `mysql_fetch_field()' repeatedly. `MYSQL_FIELD_OFFSET' This is a type-safe representation of an offset into a *MySQL* field list. (Used by `mysql_field_seek()'.) Offsets are field numbers within a row, beginning at zero. `my_ulonglong' The type used for the number of rows and for `mysql_insert_id()'. This type provides a range of `0' to `1.84e19'. The `MYSQL_FIELD' structure contains the following members: `char * name' The name of the field. `char * table' The name of the table containing this field if it isn't a calculated field. For calculated fields, the `table' value is a `NULL' pointer. `char * def' The default value of this field (set only if you use `mysql_list_fields()'). `enum enum_field_types type' The type of the field. The `type' value may be one of the following: *Type name* *Type meaning* `FIELD_TYPE_TINY' `TINYINT' field `FIELD_TYPE_ENUM' `ENUM' field `FIELD_TYPE_DECIMAL' `DECIMAL' or `NUMERIC' field `FIELD_TYPE_SHORT' `SMALLINT' field `FIELD_TYPE_LONG' `INTEGER' field `FIELD_TYPE_FLOAT' `FLOAT' field `FIELD_TYPE_DOUBLE' `DOUBLE' or `REAL' field `FIELD_TYPE_NULL' `NULL'-type field `FIELD_TYPE_TIMESTAMP'`TIMESTAMP' field `FIELD_TYPE_LONGLONG'`BIGINT' field `FIELD_TYPE_INT24' `MEDIUMINT' field `FIELD_TYPE_DATE' `DATE' field `FIELD_TYPE_TIME' `TIME' field `FIELD_TYPE_DATETIME'`DATETIME' field `FIELD_TYPE_YEAR' `YEAR' field `FIELD_TYPE_SET' `SET' field `FIELD_TYPE_BLOB' `BLOB' or `TEXT' field (use `max_length' to determine the maximum length) `FIELD_TYPE_STRING' String (`CHAR' or `VARCHAR') field `FIELD_TYPE_CHAR' Deprecated: use `FIELD_TYPE_TINY' instead The `IS_NUM()' macro allows you to test if a field has a numeric type. Pass the `type' member to `IS_NUM()' and it will evaluate to TRUE if the field is numeric: if (IS_NUM(field->type)) { printf("Field is numeric\n"); } `unsigned int length' The width of the field. `unsigned int max_length' The maximum width of the field for the selected set. If you used `mysql_list_fields()', this contains the maximum length for the field. `unsigned int flags' Different bit-flags for the field These are the bits in `flags' that you may use: *Flag name* *Flag meaning* `NOT_NULL_FLAG' Field can't be `NULL' `PRI_KEY_FLAG' Field is part of a primary key `UNIQUE_KEY_FLAG' Field is part of a unique key `MULTIPLE_KEY_FLAG' Field is part of a key `BLOB_FLAG' Field is a `BLOB' or `TEXT' `UNSIGNED_FLAG' Field is `UNSIGNED' `ZEROFILL_FLAG' Field has the `ZEROFILL' attribute `BINARY_FLAG' Field has the `BINARY' attribute `ENUM_FLAG' Field is an `ENUM' `AUTO_INCREMENT_FLAG'Field has the `AUTO_INCREMENT' attribute `TIMESTAMP_FLAG' Field is a `TIMESTAMP' The example below illustrates a typical use of the flag value: if (field->flags & NOT_NULL_FLAG) { printf("Field can't be null\n"); } You may use the following convenience macros to determine the boolean status of the `flags' member: `IS_PRI_KEY(flags)' Is this field a primary key? `IS_NOT_NULL(flags)' Is this field defined as `NOT NULL'? `IS_BLOB(flags)' Is this field a `BLOB' or `TEXT'? The use of `BLOB_FLAG', `ENUM_FLAG' and `TIMESTAMP_FLAG' is deprecated, since they indicate the type of a field rather than an attribute of the type. It is preferable to test `field->type' against `FIELD_TYPE_BLOB', `FIELD_TYPE_ENUM' or `FIELD_TYPE_TIMESTAMP' instead. `unsigned int decimals' The number of decimals for numeric fields. C API function overview ======================= The functions available in the C API are listed below. These functions are described in greater detail in the next section. *Note C API functions::. *mysql_affected_rows()* Returns the number of rows affected by the last `UPDATE', `DELETE' or `INSERT' query. *mysql_close()* Closes a server connection. *mysql_connect()* Connects to a *MySQL* server. This function is deprecated; use `mysql_real_connect()' instead. *mysql_create_db()* Creates a database. This function is deprecated; use the SQL command `CREATE DATABASE' instead. *mysql_data_seek()* Seeks to an arbitrary row in a query result set. *mysql_debug()* Does a `DBUG_PUSH' with the given string. *mysql_drop_db()* Drops a database. This function is deprecated; use the SQL command `DROP DATABASE' instead. *mysql_dump_debug_info()* Makes the server dump debug information to the log. *mysql_eof()* Determines whether or not the last row of a result set has been read. *mysql_errno()* Returns the error number from the last *MySQL* function. *mysql_error()* Returns the error message from the last *MySQL* function. *mysql_escape_string()* Escapes a string for a SQL statement. *mysql_fetch_field()* Returns the type of the next table field. *mysql_fetch_field_direct()* Returns the type of a numbered table field. *mysql_fetch_fields()* Returns an array of all field structures. *mysql_fetch_lengths()* Returns the length for all columns in the current row. *mysql_fetch_row()* Fetches the next row from the result set. *mysql_field_seek()* Puts the column cursor on a specified column. *mysql_free_result()* Frees memory used by a result set. *mysql_get_client_info()* Returns client version information. *mysql_get_host_info()* Returns a string describing the connection. *mysql_get_proto_info()* Returns the protocol version used by the connection. *mysql_get_server_info()* Returns the server version number. *mysql_info()* Information about the most recently executed query. *mysql_init()* Get or initialize a MYSQL structure. *mysql_insert_id()* Returns the last ID generated for an `AUTO_INCREMENT' field. *mysql_list_dbs()* Returns database names matching a simple regular expression. *mysql_list_fields()* Returns field names matching a simple regular expression. *mysql_list_processes()* Returns a list of the current server threads. *mysql_list_tables()* Returns table names matching a simple regular expression. *mysql_num_fields()* Returns the number of columns in a result set. *mysql_num_rows()* Returns the number of rows in a result set. *mysql_ping()* Checks if the connection to the server is working. *mysql_query()* Executes a SQL query specified as a null-terminated string. *mysql_real_connect()* Connects to a *MySQL* server. *mysql_real_query()* Executes a SQL query specified as a counted string. *mysql_reload()* Tells the server to reload the access permissions tables. *mysql_row_tell()* Returns the row cursor. *mysql_select_db()* Connects to a database. *mysql_shutdown()* Shuts down the database server. *mysql_stat()* Returns the server status as a string. *mysql_store_result()* Reads a result set to the client. *mysql_thread_id()* Returns the current thread id. *mysql_use_result()* Initiates a dynamic result set for each row. C API function descriptions =========================== In the descriptions below, a parameter or return value of `NULL' means `NULL' in the sense of the C programming language, not a *MySQL* `NULL' value. `mysql_affected_rows()' ----------------------- `my_ulonglong mysql_affected_rows(MYSQL *mysql)' Description ........... Returns the number of rows affected by the last `UPDATE', `DELETE' or `INSERT' query. May be called immediately after `mysql_query()' for `INSERT' or `UPDATE' statements. For `SELECT' statements, this works like `mysql_num_rows()'. `mysql_affected_rows()' is currently implemented as a macro. Return values ............. An integer > 0 indicates the number of rows affected or retrieved. Zero if no records matched the `WHERE' clause in the query or no query has yet been executed. -1 if the query returned an error or was called before `mysql_store_result()' was called for a `SELECT' query. Errors ...... None. Example ....... mysql_query(&mysql,"UPDATE products SET cost=cost*1.25 WHERE group=10"); printf("%d products updated",mysql_affected_rows(&mysql)); `mysql_close()' --------------- `void mysql_close(MYSQL *mysql)' Description ........... Closes a previously opened connection. Return values ............. None. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. `mysql_connect()' ----------------- `MYSQL *mysql_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd)' Description ........... This function is deprecated. It is preferable to use `mysql_real_connect()' instead. `mysql_connect()' attempts to establish a connection to a *MySQL* database engine running on `host'. The value of `host' may be either a hostname or an IP address. The `user' parameter contains the user's *MySQL* login ID, and the `passwd' parameter contains the password for `user'. NOTE: Do not attempt to encrypt `passwd' before calling `mysql_connect()'. Password encryption is handled automatically by the client API. * If `host' is `NULL' or the string `"localhost"', a connection to the local host is assumed. If the OS supports sockets (Unix) or named pipes (Win32), they are used instead of TCP/IP to connect to the server. * If `user' is `NULL', the current user is assumed. Under Windows ODBC, the current user must be specified explicitly. Under Unix, the current login name is assumed. * If `passwd' is `NULL', only records in the `user' table for the user that have a blank password field will be checked for a match. This allows the database administrator to set up the *MySQL* privilege system in such a way that users get different privileges depending on whether or not they have specified a password. `mysql_connect()' must complete successfully before you can execute any of the other API functions, with the exception of `mysql_get_client_info()'. You may optionally specify the first argument of `mysql_connect()' to be a `NULL' pointer. This will force the C API to allocate memory for the connection structure automatically and to free it when you call `mysql_close()'. The disadvantage of this approach is that you can't retrieve an error message from `mysql_connect()' if the connection fails. If the first argument is not a `NULL' pointer, it should be the address of an existing `MYSQL' structure. Return values ............. A `MYSQL*' connection handle if the connection was successful. A C `NULL' pointer if the connection was unsuccessful. Errors ...... `CR_CONN_HOST_ERROR' Failed to connect to the *MySQL* server. `CR_CONNECTION_ERROR' Failed to connect to the local *MySQL* server. `CR_IPSOCK_ERROR' Failed to create an IP socket. `CR_OUT_OF_MEMORY' Out of memory. `CR_SOCKET_CREATE_ERROR' Failed to create a Unix socket. `CR_UNKNOWN_HOST' Failed to find the IP address for the hostname. `CR_VERSION_ERROR' A protocol mismatch resulted from attempting to connect to a server with a client library that uses a different protocol version. This can happen if you use a very old client library to connect to a new server that wasn't started with the `--old-protocol' option. `CR_NAMEDPIPEOPEN_ERROR;' Failed to create a named pipe on Win32. `CR_NAMEDPIPEWAIT_ERROR;' Failed to wait for a named pipe on Win32. `CR_NAMEDPIPESETSTATE_ERROR;' Failed to get a pipe handler on Win32. Example ....... MYSQL mysql; if(!mysql_connect(&mysql, "host", "username", "password")) fprintf(stderr, "Failed to connect to database: Error: %s\n", mysql_error(&mysql)); `mysql_create_db()' ------------------- `int mysql_create_db(MYSQL *mysql, const char *db)' Description ........... Creates the database named by the `db' argument. This function is deprecated. It is preferable to use `mysql_query()' to issue a SQL `CREATE DATABASE' statement instead. Return values ............. Zero if the database was successfully created. Non-zero if an error occurred. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. Example ....... if(mysql_create_db(&mysql, "my_new_db")) fprintf(stderr, "Failed to create new database. Error: %s\n", mysql_error(&mysql)); `mysql_data_seek()' ------------------- `void mysql_data_seek(MYSQL_RES *res, unsigned int offset)' Description ........... Seeks to an arbitrary row in a query result set. This function may be used in conjunction only with `mysql_store_result)(', not with `mysql_use_result()'. The offset can be any value: `0 <= offset <= mysql_num_rows() -1' Return values ............. None. Errors ...... None. `mysql_debug()' --------------- `void mysql_debug(char *debug)' Description ........... Does a `DBUG_PUSH' with the given string. `mysql_debug()' uses the Fred Fish debug library. To use this function, you must compile the client library to support debugging. Return values ............. None. Errors ...... None. Example ....... The call shown below causes the client library to generate a trace file in `/tmp/client.trace' on the client machine: mysql_debug("d:t:O,/tmp/client.trace"); `mysql_drop_db()' ----------------- `int mysql_drop_db(MYSQL *mysql, const char *db)' Description ........... Drops the database named by the `db' argument. This function is deprecated. It is preferable to use `mysql_query()' to issue a SQL `DROP DATABASE' statement instead. Return values ............. Zero if the database was successfully dropped. Non-zero if an error occurred. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. Example ....... if(mysql_drop_db(&mysql, "some_database")) fprintf(stderr, "Failed to drop the database: Error: %s\n", mysql_error(&mysql)); `mysql_dump_debug_info()' ------------------------- `int mysql_dump_debug_info(MYSQL *mysql)' Description ........... Instructs the server to dump some debug information to the log. The connected user must have *process* privileges for this to work. Return values ............. Zero if the command was successful. Non-zero if the command failed. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. `mysql_eof()' ------------- `my_bool mysql_eof(MYSQL_RES *result)' Description ........... When `mysql_fetch_row()' returns nothing, `mysql_eof()' returns a non-zero value if the end of the result set was reached and zero if an error occurred. If an error occurred, the preferred method of finding out what the was was is to call `mysql_errno()'. `mysql_eof()' may only be used with `mysql_use_result()', not with `mysql_store_result()'. Return values ............. Zero if the end of the result set has not yet been reached. Non-zero if the end of the result set has been reached. Errors ...... None. Example ....... mysql_query(&mysql,"SELECT * FROM some_table"); result = mysql_use_result(&mysql); while((row = mysql_fetch_row(result))) { //do something with data } if(!mysql_eof(result)) { //mysql_fetch_row failed due to some error } `mysql_errno()' --------------- `unsigned int mysql_errno(MYSQL *mysql)' Description ........... Returns the error code for the last error that occurred on the connection specified by `mysql'. A return value of zero means that no error occurred. Client error message numbers are listed in `errmsg.h'. Server error message numbers are listed in `mysqld_error.h' Return values: .............. An error code value. Zero if no error has occurred. Errors ...... None. `mysql_error()' --------------- `char *mysql_error(MYSQL *mysql)' Description ........... Returns the error message, if any, describing the last *MySQL* error that occurred on the connection specified by `mysql'. An empty string is returned if no error occurred. The language of the client error messages may be changed by recompiling the *MySQL* client library. You currently can choose between English or German client error messages. Return values ............. A character string that describes the error. Errors ...... None. `mysql_escape_string()' ----------------------- `unsigned int mysql_escape_string(char *to, const char *from, unsigned int length)' Description ........... Encodes the string in `from' to an escaped SQL string that can be sent to the server in a SQL statement. The string pointed to by `from' must be `length' bytes long. You must allocate the `to' buffer to be at least `length*2+1' bytes long. When `mysql_escape_string()' returns, the contents of `to' will be a `NUL'-terminated string. *Note Base Syntax::. Characters encoded are `NUL' (ASCII 0), `\n', `\r', `\' and `''. Example ....... char query[1000],*end; end=strmov(query,"INSERT INTO test_table values("); *end++='\'' end+=mysql_escape_string(query,"What's this"); *end++='\''; *end++=',' *end++='\'' end+=mysql_escape_string(query,"binary data: \0\r\n"); *end++='\'' *end++=')'; if (mysql_real_query(&mysql,query,(int) (end-query))) { fprintf(stderr, "Failed to insert row, Error: %s\n", mysql_error(&mysql)); } The `strmov()' function above is included in the `mysqlclient' library and works like `strcpy()' but returns a pointer to the terminating null of the first argument. Return values ............. The length of the value placed into `to', not including the terminating null character. Errors ...... None. `mysql_fetch_field()' --------------------- `MYSQL_FIELD *mysql_fetch_field(MYSQL_RES *result)' Description ........... Returns the definition of one column as a `MYSQL_FIELD' structure. Call this function repeatedly to retrieve information about all columns in the result set. `mysql_fetch_field()' is reset to return information about the first field each time you execute a new `SELECT' query. The field returned by `mysql_fetch_field()' is also affected by calls to `mysql_field_seek()'. When querying for the length of a `BLOB' without retrieving a result, *MySQL* returns the `default blob length', which is 8192, when doing a `SELECT' on the table. After you retrieve a result, `column_object->max_length' contains the length of the biggest value for this column in the specific query. The 8192 size is chosen because *MySQL* doesn't know the maximum length for the `BLOB'. This should be made configurable sometime. Return values ............. The `MYSQL_FIELD' structure of the current column (`NULL' is returned if no columns are left). Errors ...... None. Example ....... MYSQL_FIELD *field; while((field = mysql_fetch_field(result))) { printf("field name %s\n", field->name); } `mysql_fetch_fields()' ---------------------- `MYSQL_FIELD *mysql_fetch_fields(MYSQL_RES * result)' Description ........... Returns an array of all `MYSQL_FIELD' structures for a result. Each structure provides the field definition for one column of the result set. Return values ............. An array of `MYSQL_FIELD' structures for all columns of a result set. Errors ...... None. Example ....... unsigned int num_fields; unsigned int i; MYSQL_FIELD *fields; num_fields = mysql_num_fields(result); fields = mysql_fetch_fields(result); for(i = 0; i < num_fields; i++) { printf("Field %u is %s\n", i, fields[i].name); } `mysql_fetch_field_direct()' ---------------------------- `MYSQL_FIELD * mysql_fetch_field_direct(MYSQL_RES * result, unsigned int fieldnr)' Description ........... Given a field number `fieldnr', returns the `fieldnr' column's field definition of a result set as a `MYSQL_FIELD' structure. `fieldnr' begins at zero. You may use this function to retrieve the definition for any arbitrary column. Return values ............. The `MYSQL_FIELD' structure of the specified column. Errors ...... None. Example ....... unsigned int num_fields; unsigned int i; MYSQL_FIELD *field; num_fields = mysql_num_fields(result); for(i = 0; i < num_fields; i++) { field = mysql_fetch_field_direct(result, i); printf("Field %u is %s\n", i, field->name); } `mysql_fetch_lengths()' ----------------------- `unsigned long *mysql_fetch_lengths(MYSQL_RES *result)' Description ........... Returns the lengths of the columns of the current row. If you have binary data, you must use this function to determine the size of the data. If you copy the data, this length information is also useful for optimization, because you can avoid calling `strlen()'. Return values ............. An array of unsigned long integers representing the size of each column (does not include terminating NUL characters). A C `NULL' pointer if there is an error. Errors ...... `NULL' is returned if you call this before calling `mysql_fetch_row()' or after retrieving all rows in the result. Example ....... MYSQL_ROW row; unsigned int * lengths; unsigned int num_fields; unsigned int i; row = mysql_fetch_row(result); if (row) { num_fields = mysql_num_fields(result); lengths = mysql_fetch_lengths(result); for(i = 0; i < num_fields; i++) { printf("Column %u is %lu bytes in length.\n", i, lengths[i]); } } `mysql_fetch_row()' ------------------- `MYSQL_ROW mysql_fetch_row(MYSQL_RES *result)' Description ........... Retrieves the next row of a result set. Returns `NULL' when there are no more rows to retrieve. When used with `mysql_use_result()', data are dynamically retrieved from the server and thus errors may occur in this situation. Return values ............. A `MYSQL_ROW' structure for the next row, or `NULL' if there is an error or there are no more rows to retrieve. Errors ...... `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. Example ....... MYSQL_ROW row; unsigned int num_fields; unsigned int i; num_fields = mysql_num_fields(result); while ((row = mysql_fetch_row(result))) { unsigned long *lengths; lengths = mysql_fetch_lengths(result); for(i = 0; i < num_fields; i++) { printf("[%.*s] ", (int) lengths[i],row[i]); } printf("\n"); } `mysql_field_seek()' -------------------- `MYSQL_FIELD_OFFSET mysql_field_seek(MYSQL_RES *result, MYSQL_FIELD_OFFSET offset)' Description ........... Sets the field cursor to the given offset. The next call to `mysql_fetch_field()' will retrieve the column associated with that offset. To seek to the beginning of a row, pass an `offset' value of zero. Return values ............. The previous value of the field cursor. Errors ...... None. `mysql_field_tell()' -------------------- `MYSQL_FIELD_OFFSET mysql_field_tell(MYSQL_RES *result)' Description ........... Returns the position of the field cursor used for the last `mysql_fetch_field()'. This value can be used as an argument to `mysql_field_seek()'. Return values ............. The current offset of the field cursor. Errors ...... None. `mysql_free_result()' --------------------- `void mysql_free_result(MYSQL_RES *result)' Description ........... Frees the memory allocated for a result set by `mysql_store_result()', `mysql_use_result()', `mysql_list_dbs()', etc. When you are done with the result set, you must free the memory it uses by calling `mysql_free_result()'. Return values ............. None. Errors ...... None. `mysql_get_client_info()' ------------------------- `char *mysql_get_client_info(void)' Description ........... Returns a string that represents the client library version. Return values ............. A character string that represents the *MySQL* client library version. Errors ...... None. `mysql_get_host_info()' ----------------------- `char *mysql_get_host_info(MYSQL *mysql)' Description ........... Returns a string describing the type of connection in use, including the server host name. Return values ............. A character string representing the server host name and the connection type. Errors ...... None. `mysql_get_proto_info()' ------------------------ `unsigned int mysql_get_proto_info(MYSQL *mysql)' Description ........... Returns the protocol version used by current connection. Return values ............. An unsigned integer representing the protocol version used by the current connection. Errors ...... None. `mysql_get_server_info()' ------------------------- `char *mysql_get_server_info(MYSQL *mysql)' Description ........... Returns a string that represents the server version number. Return values ............. A character string that represents the server version number. Errors ...... None. `mysql_info()' -------------- `char * mysql_info(MYSQL *mysql)' Description ........... Retrieves a string providing information about the most recently executed query. The format of the string varies depending on the type of query, as described below (the numbers are illustrative only; the string will contain values appropriate for the query): `INSERT INTO ... SELECT ...' String format: `Records: 100 Duplicates: 0 Warnings: 0' `LOAD DATA INFILE ...' String format: `Records: 1 Deleted: 0 Skipped: 0 Warnings: 0' `ALTER TABLE' String format: `Records: 3 Duplicates: 0 Warnings: 0' `INSERT INTO TABLE ... VALUES (...),(...),(...)...' String format: `Records: 3 Duplicates: 0 Warnings: 0' Return values ............. A character string representing additional information about the query that was most recently executed. A `NULL' pointer if no information is available for the query. Errors ...... None. `mysql_init()' -------------- `MYSQL * mysql_init(MYSQL *mysql)' Description ........... Allocates or initializes a `MYSQL' object suitable for `mysql_real_connect()'. If the argument is a `NULL' pointer, the function allocates, initializes and returns a new object, otherwise the object is initialized and the address to the object is returned. If a new object is allocated, `mysql_close()' will free this object. Return values ............. An initialized `MYSQL*' handle or a `NULL' pointer if there wasn't enough memory to allocate a new object. Errors ...... In case of low memory a `NULL' is returned. `mysql_insert_id()' ------------------- `my_ulonglong mysql_insert_id(MYSQL *mysql)' Description ........... Returns the ID generated for an `AUTO_INCREMENT' field. Use this function after you have performed an `INSERT' query into a table that contains an `AUTO_INCREMENT' field. Return values ............. The value of the last `AUTO_INCREMENT' field updated. Errors ...... None. `mysql_kill()' -------------- `int mysql_kill(MYSQL *mysql, unsigned long pid)' Description ........... Asks the server to kill the thread specified by `pid'. Return values ............. Zero on success. Non-zero on failure. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. `mysql_list_dbs()' ------------------ `MYSQL_RES *mysql_list_dbs(MYSQL *mysql, const char *wild)' Description ........... Returns a result set consisting of database names on the server that match the simple regular expression specified by the `wild' argument. `wild' may contain the wildcard characters `%' or `_', or may be a `NULL' pointer to match all databases. Calling `mysql_list_dbs()' is similar to executing the query `SHOW databases [LIKE wild]'. You must free the result set with `mysql_free_result()'. Return values ............. A `MYSQL_RES' result set for success. `NULL' if there is a failure. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_OUT_OF_MEMORY' Out of memory. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. `mysql_list_fields()' --------------------- `MYSQL_RES *mysql_list_fields(MYSQL *mysql, const char *table, const char *wild)' Description ........... Returns a result set consisting of field names in the given table that match the simple regular expression specified by the `wild' argument. `wild' may contain the wildcard characters `%' or `_', or may be a `NULL' pointer to match all fields. Calling `mysql_list_fields()' is similar to executing the query `SHOW fields FROM table [LIKE wild]'. You must free the result set with `mysql_free_result()'. Return values ............. A `MYSQL_RES' result set for success. `NULL' if there is a failure. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. `mysql_list_processes()' ------------------------ `MYSQL_RES *mysql_list_processes(MYSQL *mysql)' Description ........... Returns a result set describing the current server threads. This is the same kind of information as that reported by `mysqladmin processlist'. You must free the result set with `mysql_free_result()'. Return values ............. A `MYSQL_RES' result set for success. `NULL' if there is a failure. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. `mysql_list_tables()' --------------------- `MYSQL_RES *mysql_list_tables(MYSQL *mysql, const char *wild)' Description ........... Returns a result set consisting of table names in the current database that match the simple regular expression specified by the `wild' argument. `wild' may contain the wildcard characters `%' or `_', or may be a `NULL' pointer to match all tables. Calling `mysql_list_tables()' is similar to executing the query `SHOW tables [LIKE wild]'. You must free the result set with `mysql_free_result()'. Return values ............. A `MYSQL_RES' result set for success. `NULL' if there is a failure. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. `mysql_num_fields()' -------------------- `unsigned int mysql_num_fields(MYSQL_RES *result)' Description ........... Returns the number of columns in a result set. Return values ............. An unsigned integer representing the number of fields in a result set. Errors ...... None. `mysql_num_rows()' ------------------ `int mysql_num_rows(MYSQL_RES *result)' Description ........... Returns the number of rows in the result set. If you use `mysql_use_result()', `mysql_num_rows()' will not return the correct value until all the rows in the result set have been retrieved. Return values ............. The number of rows in the result set. Errors ...... None. `mysql_ping()' -------------- `int mysql_ping(MYSQL *mysql)' Description ........... Checks if the connection to the server is working. If it has gone down, an automatic reconnection will be attempted. This function can be used in clients that stay silent for a long while, to check (and reconnect) if the server has closed the connection. Return values ............. Zero if the server is alive. Any other value indicates an error. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_UNKNOWN_ERROR' An unknown error occurred. `mysql_query()' --------------- `int mysql_query(MYSQL *mysql, const char *query)' Description ........... Executes the SQL query pointed to by the null-terminated string `query'. `mysql_query()' cannot be used for queries that contain binary data. (Binary data may contain the `\0' character, which would be interpreted as the end of the query string.) For such cases, use `mysql_real_query()' instead. Return values ............. Zero if the query was successful. Non-zero if the query failed. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. `mysql_real_connect()' ---------------------- `MYSQL *mysql_real_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd, const char *db, uint port, const char *unix_socket, uint client_flag)' Description ........... Attempts to establish a connection to a *MySQL* database engine running on `host'. The value of `host' may be either a hostname or an IP address. The `user' parameter contains the user's *MySQL* login ID, and the `passwd' parameter contains the password for `user'. NOTE: Do not attempt to encrypt `passwd' before calling `mysql_real_connect()'. Password encryption is handled automatically by the client API. Note that before calling `mysql_real_connect()' you have to call `mysql_init()' to get or initialize a `MYSQL' structure. * If `host' is `NULL' or the string `"localhost"', a connection to the local host is assumed. If the OS supports sockets (Unix) or named pipes (Win32), they are used instead of TCP/IP to connect to the server. * If `user' is `NULL', the current user is assumed. Under Windows ODBC, the current user must be specified explicitly. Under Unix, the current login name is assumed. * If `passwd' is `NULL', only records in the `user' table for the user that have a blank password field will be checked for a match. This allows the database administrator to set up the *MySQL* privilege system in such a way that users get different privileges depending on whether or not they have specified a password. * If `db' is not `NULL', the connection will set the default database to this value. * If `port' is not 0, the value will be used as the port number for the TCP/IP connection. Note that it's the `host' parameter that decides the type of the connection. * If `unix_socket' is not `NULL', the string specifies the socket or named pipe that should be used. Note that it's the `host' parameter that decides the type of the connection. * The value of `client_flag' is usually 0, but can be set to a combination of the following flags is very special circumstances: *Flag name* *Flag meaning* `CLIENT_FOUND_ROWS'Return the number of found rows, not the number of affected rows `CLIENT_NO_SCHEMA'Don't allow the `database.table.column' `CLIENT_COMPRESS' Use compression protocol `CLIENT_ODBC' The client is an ODBC client. This changes `mysqld' to be more ODBC-friendly. `mysql_real_connect()' must complete successfully before you can execute any of the other API functions, with the exception of `mysql_get_client_info()'. You may optionally specify the first argument of `mysql_real_connect()' to be a `NULL' pointer. This will force the C API to allocate memory for the connection structure automatically and to free it when you call `mysql_close()'. The disadvantage of this approach is that you can't retrieve an error message from `mysql_real_connect()' if the connection fails. If the first argument is not a `NULL' pointer, it should be the address of an existing `MYSQL' structure. Return values ............. A `MYSQL*' connection handle if the connection was successful. A C `NULL' pointer if the connection was unsuccessful. Errors ...... `CR_CONN_HOST_ERROR' Failed to connect to the *MySQL* server. `CR_CONNECTION_ERROR' Failed to connect to the local *MySQL* server. `CR_IPSOCK_ERROR' Failed to create an IP socket. `CR_OUT_OF_MEMORY' Out of memory. `CR_SOCKET_CREATE_ERROR' Failed to create a Unix socket. `CR_UNKNOWN_HOST' Failed to find the IP address for the hostname. `CR_VERSION_ERROR' A protocol mismatch resulted from attempting to connect to a server with a client library that uses a different protocol version. This can happen if you use a very old client library to connect to a new server that wasn't started with the `--old-protocol' option. `CR_NAMEDPIPEOPEN_ERROR;' Failed to create a named pipe on Win32. `CR_NAMEDPIPEWAIT_ERROR;' Failed to wait for a named pipe on Win32. `CR_NAMEDPIPESETSTATE_ERROR;' Failed to get a pipe handler on Win32. Example ....... NEED EXAMPLE HERE `mysql_real_query()' -------------------- `int mysql_real_query(MYSQL *mysql, const char *query, unsigned int length)' Description ........... Executes the SQL query pointed to by query, which should be a string `length' bytes long. You *must* use `mysql_real_query()' for queries that contain binary data, since binary data may contain the `\0' character. In addition, `mysql_real_query()' is faster than `mysql_query()' since it does not call `strlen()' on the query. Return values ............. Zero if the query was successful. Non-zero if the query failed. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. `mysql_reload()' ---------------- `int mysql_reload(MYSQL *mysql)' Description ........... Asks the *MySQL* server to reload the access permissions tables. The connected user must have *reload* privileges. Return values ............. Zero on success. Non-zero on failure. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. `mysql_row_tell()' ------------------ `unsigned int mysql_row_tell(MYSQL_RES *result)' Description ........... Returns the current position of the row cursor for the last `mysql_fetch_row()'. This value can be used as an argument to `mysql_row_seek()'. Return values ............. The current offset of the row cursor. Errors ...... None. `mysql_select_db()' ------------------- `int mysql_select_db(MYSQL *mysql, const char *db)' Description ........... Instructs the current connection specified by `mysql' to use the database specified by `db' as the default (current) database. In subsequent queries, this database becomes the default for table references that do not indicate an explicit database specifier. `mysql_select_db()' fails unless the connected user can be authenticated as having permission to use the database. Return values ............. Zero on success. Non-zero on failure. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. `mysql_shutdown()' ------------------ `int mysql_shutdown(MYSQL *mysql)' Description ........... Asks the database server to shutdown. The connected user must have *shutdown* privileges. Return values ............. Zero on success. Non-zero on failure. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. `mysql_stat()' -------------- `char *mysql_stat(MYSQL *mysql)' Description ........... Returns information similar to that provided by `mysqladmin status' as a character string. This includes uptime in seconds and the number of running threads, questions, reloads and open tables. Return values ............. A character string describing the server status. `NULL' if the command failed. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. `mysql_store_result()' ---------------------- `MYSQL_RES *mysql_store_result(MYSQL *mysql)' Description ........... Reads the result of a query to the client, allocates a `MYSQL_RES' structure, and places the results into this structure. You must call `mysql_store_result()' or `mysql_use_result()' after every query which successfully retrieves data. An empty result set is returned if there are no rows returned. You must call `mysql_free_result()' once you are done with the result set. Return values ............. A `MYSQL_RES' result structure with the results. `NULL' if there was an error. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_OUT_OF_MEMORY' Out of memory. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. `mysql_thread_id()' ------------------- `unsigned long mysql_thread_id(MYSQL * mysql)' Description ........... Returns the thread id of the current connection. This value can be used as an argument to `mysql_kill()' to kill the thread. Return values ............. The thread id of the current connection. Errors ...... None. `mysql_use_result()' -------------------- `MYSQL_RES *mysql_use_result(MYSQL *mysql)' Description ........... `mysql_use_result()' reads the result of a query directly from the server without storing it in a temporary table or local buffer. This is somewhat faster and uses much less memory than `mysql_store_result()'. In this case the client will only allocate memory for the current row and a communication buffer of size `max_allowed_packet'. On the other hand, you shouldn't use `mysql_use_result()' if you are doing a lot of processing for each row at the client side, or if the output is sent to a screen on which the user may type a `^S' (stop scroll). This would tie up the server and then other threads couldn't update the used tables. When using `mysql_use_result()', you must execute `mysql_fetch_row()' until you get back a `NULL' value, otherwise the next query will get results from the previous query. The C API will give the error `Commands out of sync; You can't run this command now' if you forget to do this! You may not use `mysql_data_seek()', `mysql_num_rows()' or `mysql_affected_rows()' with a result returned from `mysql_use_result()', nor may you issue other queries until the `mysql_use_result()' has finished. You must call `mysql_free_result()' once you are done with the result set. Return values ............. A `MYSQL_RES' result structure. `NULL' if there was an error. Errors ...... `CR_COMMANDS_OUT_OF_SYNC' Commands were executed in an improper order. `CR_OUT_OF_MEMORY' Out of memory. `CR_SERVER_GONE_ERROR' The *MySQL* server has gone away. `CR_SERVER_LOST' The connection to the server was lost during the query. `CR_UNKNOWN_ERROR' An unknown error occurred. Why is it that after `mysql_query()' returns success, `mysql_store_result()' sometimes returns `NULL?' ------------------------------------------------------------------------------------------------------ It is possible for `mysql_store_result()' to return `NULL' following a successful call to `mysql_query()'. When this happens, it means one of the following conditions occurred: * There was a `malloc()' failure. * The data couldn't be read (error on connection). * The query returned no data (`INSERT', `UPDATE' or `DELETE'). You can always check whether or not the statement should have produced a non-empty result by calling `mysql_num_fields()'. If `mysql_num_fields()' returns zero, the result is empty and the last query was a statement that does not return values (for example, an `INSERT' or a `DELETE'). If `mysql_num_fields()' returns a non-zero value, the statement should have produced a non-empty result. You can also test for an error by calling `mysql_error()' or `mysql_errno()'. What results can I get from a query? ------------------------------------ In addition to the result set returned by a query, you can also get the following information: * `mysql_affected_rows()' returns the number of affected rows in the last query when doing an `INSERT', `UPDATE' or `DELETE'. An exception is that if `DELETE' is used without a `WHERE' clause, the table is truncated, which is much faster! In this case, `mysql_affected_rows()' returns zero for the number of records affected. * `mysql_insert_id()' returns the ID generated by the last query that inserted a row into a table with an `AUTO_INCREMENT' index. *Note `mysql_insert_id()': mysql_insert_id. * Some queries (`LOAD DATA INFILE ...', `INSERT INTO ... SELECT ...', `UPDATE') return additional info. The result is returned by `mysql_info()'. `mysql_info()' returns a `NULL' pointer if there is no additional information. How can I get the unique ID for the last inserted row? ------------------------------------------------------ If you insert a record in a table containing a column that has the `AUTO_INCREMENT' attribute, you can get the given ID with the `mysql_insert_id()' function. You can also retrieve the ID by using the `LAST_INSERT_ID()' function in a query string that you pass to `mysql_query()'. You can check if an `AUTO_INCREMENT' index is used by executing the following code. This also checks if the query was an `INSERT' with an `AUTO_INCREMENT' index: if (mysql_error(MYSQL)[0] == 0 && mysql_num_fields(MYSQL_RESULT) == 0 && mysql_insert_id(MYSQL) != 0) used_id = mysql_insert_id(MYSQL); The last ID that was generated is maintained in the server on a per-connection basis. It will not be changed by another client. It will not even be changed if you update another `AUTO_INCREMENT' column with a non-magic value (that is, a value that is not `NULL' and not 0). Problems linking with the C API ------------------------------- When linking with the C API, you can get the following errors on some systems: gcc -g -o client test.o -L/usr/local/lib/mysql -lmysqlclient -lsocket -lnsl Undefined first referenced symbol in file floor /usr/local/lib/mysql/libmysqlclient.a(password.o) ld: fatal: Symbol referencing errors. No output written to client This means that on your system you must include the math library (`-lm') at the end of the compile/link line. How to make a thread-safe client -------------------------------- The client is `almost' thread-safe. The biggest problem is that `net.c' (the file containing the subroutines that read from sockets) is not interrupt-safe. This was done with the thought that you might want to have your own alarm that can break a long read to a server. The standard client libraries are not compiled with the thread options. To get a thread-safe client, use the `-lmysys', `-lstring' and `-ldbug' libraries and `net_serv.o' that the server uses. When using a threaded client, you can make great use of the the routines in the `thr_alarm.c' file. If you are using routines from the `mysys' library, the only thing you must remember is to call `my_init()' first! All functions except `mysql_connect()' are currently thread-safe. To make `mysql_connect()' thread-safe, you must recompile the client with this command: shell> CPPFLAGS=-DTHREAD_SAFE_CLIENT ./configure ... You may get some errors because of undefined symbols when linking the standard client, because the pthread libraries are not included by default. The resulting `libmysqld.a' library is now thread-safe. Two threads can't use the same connection handle (returned by `mysql_connect()') at the same time, even if two threads can use different `MYSQL_RES' pointers that were created with `mysql_store_result()'. *MySQL* Perl API's ================== Since `DBI'/`DBD' now is the recommended Perl interface, `mysqlperl' is not documented here. `DBI' with `DBD::mysql' ----------------------- `DBI' is a generic interface for many databases. That means that you can write a script that works with many different database engines without change. You need a DataBase Driver (DBD) defined for each database type. For *MySQL*, this driver is called `DBD::mysql'. For more information on the Perl5 DBI, please visit the `DBI' web page and read the documentation: `http://www.hermetica.com/technologia/DBI/' For more information on Object Oriented Programming (OOP) as defined in Perl5, see the Perl OOP page: `http://language.perl.com/info/documentation.html' The `DBI' interface ................... *Portable DBI methods* `connect' Establishes a connection to a database server `prepare' Prepares a SQL statement for execution `do' Prepares and executes a SQL statement `disconnect' Disconnects from the database server `quote' Quotes string or `BLOB' values to be inserted `execute' Executes prepared statements `fetchrow_array' Fetches the next row as an array of fields. `fetchrow_arrayref' Fetches next row as a reference array of fields `fetchrow_hashref' Fetches next row as a reference to a hashtable `fetchall_arrayref' Fetches all data as an array of arrays `finish' Finishes a statement and let the system free resources `rows' Returns the number of rows affected `data_sources' Returns an array of databases available on localhost `ChopBlanks' Controls whether `fetchrow_*' methods trim spaces `NUM_OF_PARAMS' The number of placeholders in the prepared statement `NULLABLE' Which columns can be `NULL' *MySQL-specific methods* `insertid' The latest `AUTO_INCREMENT' value `is_blob' Which column are `BLOB' values `is_key' Which columns are keys `is_num' Which columns are numeric `is_pri_key' Which columns are primary keys `is_not_null' Which columns CANNOT be `NULL'. See `NULLABLE'. `length' Maximum possible column sizes `max_length' Maximum column sizes actually present in result `NAME' Column names `NUM_OF_FIELDS' Number of fields returned `table' Table names in returned set `type' All column types `_CreateDB' Create a database `_DropDB' Drop a database. *THIS IS DANGEROUS.* The Perl methods are described in more detail in the following sections: *Portable DBI methods* `connect($data_source, $username, $password)' Use the `connect' method to make a database connection to the data source. The `$data_source' value should begin with `DBI:driver_name:'. Example uses of `connect' with the `DBD::mysql' driver: $dbh = DBI->connect("DBI:mysql:$database", $user, $password); $dbh = DBI->connect("DBI:mysql:$database:$hostname", $user, $password); $dbh = DBI->connect("DBI:mysql:$database:$hostname:$port", $user, $password); If the user name and/or password are undefined, `DBI' uses the values of the `DBI_USER' and `DBI_PASS' environment variables, respectively. If you don't specify a hostname, it defaults to `'localhost''. If you don't specify a port number, it defaults to the default *MySQL* port (3306). `prepare($statement)' Prepares a SQL statement for execution by the database engine and returns a statement handle `($sth)' which you can use to invoke the `execute' method. Example: $sth = $dbh->prepare($statement) or die "Can't prepare $statement: $dbh->errstr\n"; `do($statement)' The `do' method prepares and executes a SQL statement and returns the number of rows affected. This method is generally used for "non-select" statements which cannot be prepared in advance (due to driver limitations) or which do not need to executed more than once (inserts, deletes, etc.). Example: $rc = $dbh->do($statement) or die "Can't execute $statement: $dbh- >errstr\n"; `disconnect' The `disconnect' method disconnects the database handle from the database. This is typically called right before you exit from the program. Example: $rc = $dbh->disconnect; `quote($string)' The `quote' method is used to "escape" any special characters contained in the string and to add the required outer quotation marks. Example: $sql = $dbh->quote($string) `execute' The `execute' method executes the prepared statement. For non-`SELECT' statements, it returns the number of rows affected. For `SELECT' statements, `execute' only starts the SQL query in the database. You need to use one of the `fetch_*' methods described below to retrieve the data. Example: $rv = $sth->execute or die "can't execute the query: $sth->errstr; `fetchrow_array' This method fetches the next row of data and returns it as an array of field values. Example: while(@row = $sth->fetchrow_array) { print qw($row[0]\t$row[1]\t$row[2]\n); } `fetchrow_arrayref' This method fetches the next row of data and returns it as a reference to an array of field values. Example: while($row_ref = $sth->fetchrow_arrayref) { print qw($row_ref->[0]\t$row_ref->[1]\t$row_ref->[2]\n); } `fetchrow_hashref' This method fetches a row of data and returns a reference to a hash table containing field name/value pairs. This method is not nearly as efficient as using array references as demonstrated above. Example: while($hash_ref = $sth->fetchrow_hashref) { print qw($hash_ref->{firstname}\t$hash_ref->{lastname}\t\ $hash_ref- > title}\n); } `fetchall_arrayref' This method is used to get all the data (rows) to be returned from the SQL statement. It returns a reference to an array of arrays of references to each row. You access/print the data by using a nested loop. Example: my $table = $sth->fetchall_arrayref or die "$sth->errstr\n"; my($i, $j); for $i ( 0 .. $#{$table} ) { for $j ( 0 .. $#{$table->[$i]} ) { print "$table->[$i][$j]\t"; } print "\n"; } `finish' Indicates that no more data will be fetched from this statement handle. You call this method to free up the statement handle and any system resources it may be holding. Example: $rc = $sth->finish; `rows' Returns the number of rows affected (updated, deleted, etc.) from the last command. This is usually used after a `do' or non-`SELECT' `execute' statement. Example: $rv = $sth->rows; `NULLABLE' Returns a reference to an array of boolean values; for each element of the array, a value of TRUE indicates that this column may contain `NULL' values. Example: $null_possible = $sth->{NULLABLE}; `NUM_OF_FIELDS' This attribute indicates the number of fields returned by a `SELECT' or `SHOW FIELDS' statement. You may use this for checking whether a statement returned a result: A zero value indicates a non-`SELECT' statement like `INSERT', `DELETE' or `UPDATE'. Example: $nr_of_fields = $sth->{NUM_OF_FIELDS}; `data_sources($driver_name)' This method returns an array containing names of databases available to the *MySQL* server on the host `'localhost''. Example: @dbs = DBI->data_sources("mysql"); `ChopBlanks' This attribute determines whether the `fetchrow_*' methods will chop leading and trailing blanks from the returned values. Example: $sth->{'ChopBlanks'} =1; *MySQL-specific methods* `insertid' If you use the `AUTO_INCREMENT' feature of *MySQL*, the new auto-incremented values will be stored here. Example: $new_id = $sth->{insertid}; `is_blob' Returns a reference to an array of boolean values; for each element of the array, a value of TRUE indicates that the respective column is a `BLOB'. Example: $keys = $sth->{is_blob}; `is_key' Returns a reference to an array of boolean values; for each element of the array, a value of TRUE indicates that the respective column is a key. Example: $keys = $sth->{is_key}; `is_num' Returns a reference to an array of boolean values; for each element of the array, a value of TRUE indicates that the respective column contains numeric values. Example: $nums = $sth->{is_num}; `is_pri_key' Returns a reference to an array of boolean values; for each element of the array, a value of TRUE indicates that the respective column is a primary key. Example: $pri_keys = $sth->{is_pri_key}; `is_not_null' Returns a reference to an array of boolean values; for each element of the array, a value of FALSE indicates that this column may contain `NULL' values. Example: $not_nulls = $sth->{is_not_null}; It is preferable to use the `NULLABLE' attribute (described above), since that is a DBI standard. `length' `max_length' Each of these methods returns a reference to an array of column sizes. The `length' array indicates the maximum possible sizes that each column may be (as declared in the table description). The `max_length' array indicates the maximum sizes actually present in the result table. Example: $lengths = $sth->{length}; $max_lengths = $sth->{max_length}; `NAME' Returns a reference to an array of column names. Example: $names = $sth->{NAME}; `table' Returns a reference to an array of table names. Example: $tables = $sth->{table}; `type' Returns a reference to an array of column types. Example: $types = $sth->{type}; `_CreateDB' Creates a database. This method is deprecated. It is preferable to issue a `CREATE DATABASE' statement using the `do' method instead, since `do' is a DBI standard. `_DropDB' Drops a database. *THIS IS DANGEROUS.* This method is deprecated. It is preferable to issue a `DROP DATABASE' statement using the `do' method instead, since `do' is a DBI standard. More `DBI'/`DBD' information ............................ You can use the `perldoc' command to get more information about `DBI'. perldoc DBI perldoc DBI::FAQ perldoc mysql You can also use the `pod2man', `pod2html', etc., tools to translate to other formats. And of course you can find the latest `DBI' information at the `DBI' web page: `http://www.hermetica.com/technologia/DBI/' *MySQL* Java connectivity (JDBC) ================================ There are 2 supported JDBC drivers for MySQL (the twz and mm driver). You can find a copy of these at `http://www.tcx.se/Contrib'. For documentation consult any JDBC documentation and the drivers own documentation for *MySQL* specific features. *MySQL* PHP API's ================= PHP documentation (http://www.php.net/manual/ref.mysql.php3). *MySQL* C++ API's ================= Insert pointers/descriptions for C++. *MySQL* Python API's ==================== The `http://www.tcx.se/Contrib,Contrib' directory contains a Python interface written by Joseph Skinner. *MySQL* TCL API's ================= `http://www.binevolve.com/~tdarugar/tcl-sql/, TCL at binevolve' The `http://www.tcx.se/Contrib,Contrib' directory contains a TCL interface that is based on msqltcl 1.50. How *MySQL* compares to other databases *************************************** How *MySQL* compares to `mSQL' ============================== This section has been written by the *MySQL* developers, so it should be read with that in mind. But there are NO factual errors that we know of. For a list of all supported limits, functions and types, see the `crash-me' web page (http://www.tcx.se/crash-me-choose.htmy). *Performance* For a true comparison of speed, consult the growing *MySQL* benchmark suite. *Note Benchmarks::. Because there is no thread creation overhead, a small parser, few features and simple security, `mSQL' should be quicker at: * Tests that perform repeated connects and disconnects, running a very simple query during each connection. * `INSERT' operations into very simple tables with few columns and keys. * `CREATE TABLE' and `DROP TABLE'. * `SELECT' on something that isn't an index. (A table scan is very easy.) Since these operations are so simple, it is hard to be better at them when you have a higher startup overhead. After the connection is established, *MySQL* should perform much better. On the other hand, *MySQL* is much faster than `mSQL' (and most other SQL implementions) on the following: * Complex `SELECT' operations. * Retrieving large results (*MySQL* has a better, faster and safer protocol). * Tables with variable-length strings, since *MySQL* has more efficent handling and can have indexes on `VARCHAR' columns. * Handling tables with many columns. * Handling tables with large record lengths. * `SELECT' with many expressions. * `SELECT' on large tables. * Handling many connections at the same time. *MySQL* is fully multi-threaded. Each connection has its own thread, which means that no thread has to wait for another (unless a thread is modifying a table another thread wants to access.) In `mSQL', once one connection is established, all others must wait until the first has finished, regardless of whether the connection is running a query that is short or long. When the first connection terminates, the next can be served, while all the others wait again, etc. * Joins. `mSQL' can become pathologically slow if you change the order of tables in a `SELECT'. In the benchmark suite, a time more than 15000 times slower than *MySQL* was seen. This is due to `mSQL''s lack of a join optimizer to order tables in the optimal order. However, if you put the tables in exactly the right order in `mSQL' 2, the join will be relatively fast! *Note Benchmarks::. * `ORDER BY' and `GROUP BY'. * `DISTINCT'. * Using `TEXT' or `BLOB' columns. *SQL Features* * `GROUP BY' and `HAVING'. `mSQL' does not support `GROUP BY' at all. *MySQL* supports a full `GROUP BY' with both `HAVING' and the following functions: `COUNT()', `AVG()', `MIN()', `MAX()', `SUM()' and `STD()'. `COUNT(*)' is optimized to return very quickly if the `SELECT' retrieves from one table, no other columns are retrieved and there is no `WHERE' clause. `MIN()' and `MAX()' may take string arguments. * `INSERT' and `UPDATE' with calculations. *MySQL* can do calculations in an `INSERT' or `UPDATE'. For example: mysql> UPDATE SET x=x*10+y WHERE x<20; * Aliasing. *MySQL* has column aliasing. * Qualifying column names. In *MySQL*, if a column name is unique among the tables used in a query, you do not have to use the full qualifier. * `SELECT' with functions. *MySQL* has many functions (too many to list here; see *Note Functions::). *Disk space efficiency* That is, how small can you make your tables? *MySQL* has very precise types, so you can create tables that take very little space. An example of a useful *MySQL* datatype is the `MEDIUMINT' that is 3 bytes long. If you have 100,000,000 records, saving even one byte per record is very important. `mSQL2' has a more limited set of column types, so it is more difficult to get small tables. *Stability* This is harder to judge objectively. For a discussion of *MySQL* stability, see *Note Stability::. We have no experience with `mSQL' stability, so we cannot say anything about that. *Price* Another important issue is the license. *MySQL* has a more flexible license than `mSQL', and is also less expensive than `mSQL'. Whichever product you choose to use, remember to at least consider paying for a license or email support. (You are required to get a license if you include *MySQL* with a product that you sell, of course.) *Perl interfaces* *MySQL* has basically the same interfaces to Perl as `mSQL' with some added features. *JDBC (Java)* *MySQL* currently has 4 JDBC drivers: * The gwe driver: A Java interface by GWE technologies (not supported anymore). * The jms driver: An improved gwe driver by Xiaokun Kelvin ZHU . * The twz driver: A type 4 JDBC driver by Terrence W. Zellers . This is commercial but is free for private and educational use. * The mm driver: A type 4 JDBC driver by Mark Matthews . This is released under the GPL. The recommended drivers are the twz or mm driver. Both are reported to work excellently. We know that `mSQL' has a JDBC driver, but we have too little experience with it to compare. *Rate of development* *MySQL* has a very small team of developers, but we are quite used to coding C and C++ very rapidly. Since threads, functions, `GROUP BY' and so on are still not implemented in `mSQL', it has a lot of catching up to do. To get some perspective on this, you can view the `mSQL' `HISTORY' file for the last year and compare it with the News section of the *MySQL* Reference Manual (*note News::.). It should be pretty obvious which one has developed most rapidly. *Utility programs* Both `mSQL' and *MySQL* have many interesting third-party tools. Since it is very easy to port upward (from `mSQL' to *MySQL*), almost all the interesting applications that are available for `mSQL' are also available for *MySQL*. *MySQL* comes with a simple `msql2mysql' program that fixes differences in spelling between `mSQL' and *MySQL* for the most-used C API functions. For example, it changes instances of `msqlConnect()' to `mysql_connect()'. Converting a client program from `mSQL' to *MySQL* usually takes a couple of minutes. How to convert `mSQL' tools for *MySQL* --------------------------------------- According to our experience, it would just take a few hours to convert tools such as `msql-tcl' and `msqljava' that use the `mSQL' C API so that they work with the *MySQL* C API. The conversion procedure is: 1. Run the shell script `msql2mysql' on the source. This requires the `replace' program, which is distributed with *MySQL*. 2. Compile. 3. Fix all compiler errors. Differences between the `mSQL' C API and the *MySQL* C API are: * *MySQL* uses a `MYSQL' structure as a connection type (`mSQL' uses an `int'). * `mysql_connect()' takes a pointer to a `MYSQL' structure as a parameter. It is easy to define one globally or to use `malloc()' to get one. `mysql_connect()' also takes 2 parameters for specifying the user and password. You may set these to `NULL, NULL' for default use. * `mysql_error()' takes the `MYSQL' structure as a parameter. Just add the parameter to your old `msql_error()' code if you are porting old code. * *MySQL* returns an error number and a text error message for all errors. `mSQL' returns only a text error message. * Some incompatibilities exist as a result of *MySQL* supporting multiple connections to the server from the same process. How `mSQL' and *MySQL* client/server communications protocols differ -------------------------------------------------------------------- There are enough differences that it is impossible (or at least not easy) to support both. The most significant ways in which the *MySQL* protocol differs from the `mSQL' protocol are listed below: * A message buffer may contain many result rows. * The message buffers are dynamically enlarged if the query or the result is bigger than the current buffer, up to a configurable server and client limit. * All packets are numbered to catch duplicated or missing packets. * All column values are sent in ASCII. The lengths of columns and rows are sent in packed binary coding (1, 2 or 3 bytes). * *MySQL* can read in the result unbuffered (without having to store the full set in the client). * If a single write/read takes more than 30 seconds, the server closes the connection. * If a connection is idle for 8 hours, the server closes the connection. How `mSQL' 2.0 SQL syntax differs from *MySQL* ---------------------------------------------- *Column types* `*MySQL*' Has the following additional types (among others; see *Note Create table::): * `ENUM' type for one of a set of strings. * `SET' type for many of a set of strings. * `BIGINT' type for 64-bit integers. `' *MySQL* also supports the following additional type attributes: * `UNSIGNED' option for integer columns. * `ZEROFILL' option for integer columns. * `AUTO_INCREMENT' option for integer columns that are a `PRIMARY KEY'. *Note `mysql_insert_id()': mysql_insert_id. * `DEFAULT' value for all columns. `mSQL2' `mSQL' column types correspond to the *MySQL* types shown below: `mSQL' *Corresponding *MySQL* type* *type* `CHAR(len)'`CHAR(len)' `TEXT(len)'`TEXT(len)'. `len' is the maximal length. And `LIKE' works. `INT' `INT'. With many more options! `REAL' `REAL'. Or `FLOAT'. Both 4- and 8-byte versions are available. `UINT' `INT UNSIGNED' `DATE' `DATE'. Uses ANSI SQL format rather than `mSQL''s own. `TIME' `TIME' `MONEY' `DECIMAL(12,2)'. A fixed-point value with two decimals. *Index creation* `*MySQL*' Indexes may be specified at table creation time with the `CREATE TABLE' statement. `mSQL' Indexes must be created after the table has been created, with separate `CREATE INDEX' statements. *To insert a unique identifier into a table* `*MySQL*' Use `AUTO_INCREMENT' as a column type specifier. *Note `mysql_insert_id()': mysql_insert_id. `mSQL' Create a `SEQUENCE' on a table and select the `_seq' column. *To obtain a unique identifier for a row* `*MySQL*' Add a `PRIMARY KEY' or `UNIQUE' key to the table. `mSQL' Use the `_rowid' column. Observe that `_rowid' may change over time depending on many factors. *To get the time a column was last modified* `*MySQL*' Add a `TIMESTAMP' column to the table. This column is automatically set to the current time for `INSERT' or `UPDATE' statements if you don't give the column a value or if you give it a `NULL' value. `mSQL' Use the `_timestamp' column. *`NULL' value comparisons* `*MySQL*' *MySQL* follows ANSI SQL and a comparison with `NULL' is always `NULL'. `mSQL' In `mSQL', `NULL = NULL' is TRUE. You must change `=NULL' to `IS NULL' and `<>NULL' to `IS NOT NULL' when porting old code from `mSQL' to *MySQL*. *String comparisons* `*MySQL*' Normally, string comparisons are performed in case-independent fashion with the sort order determined by the current character set (ISO-8859-1 Latin1 by default). If you don't like this, declare your columns with the `BINARY' attribute, which causes comparisons to be done according to the ASCII order used on the *MySQL* server host. `mSQL' All string comparisons are performed in case-sensitive fashion with sorting in ASCII order. *Case-insensitive searching* `*MySQL*' `LIKE' is a case-insensitive or case-sensitive operator, depending on the columns involved. If possible, *MySQL* uses indexes if the `LIKE' argument doesn't start with a wildcard character. `mSQL' Use `CLIKE'. *Handling of trailing spaces* `*MySQL*' Strips all spaces at the end of `CHAR' and `VARCHAR' columns. Use a `TEXT' column if this behavior is not desired. `mSQL' Retains trailing space. *`WHERE' clauses* `*MySQL*' *MySQL* correctly prioritizes everything (`AND' is evaluated before `OR'). To get `mSQL' behavior in *MySQL*, use parentheses (as shown below). `mSQL' Evaluates everything from left to right. This means that some logical calculations with more than three arguments cannot be expressed in any way. It also means you must change some queries when you upgrade to *MySQL*. You do this easily by adding parentheses. Suppose you have the following `mSQL' query: mysql> SELECT * FROM table WHERE a=1 AND b=2 OR a=3 AND b=4; To make *MySQL* evaluate this the way that `mSQL' would, you must add parentheses: mysql> SELECT * FROM table WHERE (a=1 AND (b=2 OR (a=3 AND (b=4)))); *Access control* `*MySQL*' Has tables to store grant (permission) options per user, host and database. *Note Privileges::. `mSQL' Has a file `mSQL.acl' in which you can grant read/write privileges for users. `' How *MySQL* compares to PostgreSQL ================================== `PostgreSQL' has some more advanced features like user-defined types, triggers, rules and transactions. But it lacks many of the standard types and functions from ANSI SQL and ODBC. See the `crash-me' web page (http://www.tcx.se/crash-me-choose.htmy) for a complete list of which limits, types and functions are supported or unsupported. Normally, `PostgreSQL' is much slower than *MySQL*. *Note Benchmarks::. This is due largely to their transactions system. If you really need transactions and can afford to pay the speed penalty, you should take a look at PostgreSQL. Some *MySQL* users ****************** Some Web search engines ----------------------- * AAA Matilda Web Search (http://www.aaa.com.au) * What's New (http://www.whatsnu.com/) * Aladin (http://www.aladin.de/) * Columbus Finder (http://www.columbus-finder.de/) * Spider (http://www.spider.de/) * Blitzsuche (http://www.blitzsuche.de/) * Indoseek Indonesia (http://www.indoseek.co.id) * Yaboo - Yet Another BOOkmarker (http://www.yaboo.dk/) Some Information search engines concentrated on some area --------------------------------------------------------- * Jobvertise: Post and search for jobs (http://www.jobvertise.com) * The Music Database (http://www.musicdatabase.com) * Fotball (Soccer) search page (http://www.soccersearch.com) * TAKEDOWN - wrestling (http://www.headrush.net/takedown) * The International Lyrics Network (http://www.lyrics.net) * Musicians looking for other musicians (Free Service) (http://TheMatrix.com/~matrix/band_search.phtml) * AddALL books searching and price comparison (http://www.addall.com/AddBooks/Stores.html) * Harvard's Gray Herbarium Index of Plant Names (http://www.herbaria.harvard.edu/Data/Gray/gray.html) * Research Publications at Monash University in Australia (http://www.csse.monash.edu.au/publications/) * The Game Development Search Engine (http://www.game-developer.com/) Some Domain/Internet/Web and related services --------------------------------------------- * Registry of Web providers that support *MySQL* (http://www.wix.com/mysql-hosting) * Monolith Internet Services (http://www.ml.org) runs *MySQL* supporting nearly a million rows and over 100,000 users. * Online Database (http://worldcommunity.com/) * BigBiz Internet Services (http://www.bigbiz.com) * The Virt Gazette (http://virt.circle.net) * Global InfoNet Inc (http://www.california.com) * WebHosters - A Guide to WWW Providers (http://www.webhosters.com) * Internet information server (http://online.dn.ru) * A pro-Linux/tech news and comment/discussion site (http://www.slashdot.org) * WorldNet Communications - An Internet Services Provider (http://www.worldnetla.net) * Web consultant for net citizens (http://www.netizen.com.au/) * Search site for training courses in the UK (http://www.trainingpages.co.uk) * Gannon Chat (GPL). Written in Perl and Javascript (http://chat.nitco.com) * A general links directory (http://www.addurls.com/) * A web-based bookmark management service (http://www.bookmarktracker.com) Web sites that use `PHP' and *MySQL* ------------------------------------ * Jgaa's Internet - Official Support Site (http://war.jgaa.com:8080/support/index.php3) running via apache * Ionline - online publication: (http://io.incluso.com) *MySQL*, PHP, Java, Web programming, DB development * BaBoo(Browse and bookmark). Free web-based bookmark manager and Calendar (http://www.baboo.com) * Course Schedule System at Pensacola Junior College (http://www.courses.pjc.cc.fl.us/Schedule/index.php) Uncategorized pages ------------------- * AZC.COM's Feature Showcase (http://www.feature-showcase.com/htmls/demo_mysql.sql) * Course Search (http://www.teach.org.uk/subjects/trainingcourse/g.html) * Northerbys Online Auctions (http://www.northerbys.com) * Amsterdam Airport Schiphol (http://www.schiphol.nl/flights/home.htm) * CD database (http://TheMatrix.com/seventhsin/query.phtml) * Used Audio Gear Database (http://TheMatrix.com/~flmm/GEAR.html) * Musical note-sheets (http://www.kiss.de/musik-mueller) * Bagism - A John Lennon fan page (http://www.bagism.com) * US Folk art broker (http://www.selftaught.com/) * Mail reading on the web (http://organizer.net/) * Free home pages on www.somecoolname.mypage.org (http://www.mypage.org/) * Der Server f"ur Schulen im Web (In German) (http://www.schulweb.de/) * Auldhaefen Online Services (http://www.ald.net/) * CaryNET Information Center (http://www.cary.net/) * Dataden Computer Systems (http://www.dataden.com/) * Andr'emuseet (In Swedish) (http://andree.grm.se/) * HOMESITE Internet Marketing (http://www.him.net/) * Jade-V Network Services (http://www.jade-v.com/techinfo.html) * http://ww2010.atmos.uiuc.edu/(Gl)/abt/aknw/tech.rxml, Weather World 2010 Technical Credits convert to `mSQL' v1 and v2, and is free of charge for anyone. See `http://www.cynergi.net/prod/exportsql/' for latest version. By Pedro Freire, . Note: Doesn't work with Access2 ! findres.pl (http://www.tcx.se/Contrib/findres.pl) Find reserved words in tables. By Nem W Schlecht. genquery.zip (http://www.tcx.se/Contrib/genquery.zip) `http://www.odbsoft.com/cook/sources.htm' This package has various functions for generating html code from an SQL table structure and for generating SQL statements (Select, Insert, Update, Delete) from an html form. You can build a complete forms interface to an SQL database (query, add, update, delete) without any programming! By Marc Beneteau, . handicap.tar.gz (http://www.tcx.se/Contrib/handicap.tar.gz) Performance handicapping system for yachts. Uses PHP. By . hylalog-1.0.tar.gz (http://www.tcx.se/Contrib/hylalog-1.0.tar.gz) Store `hylafax' outgoing faxes in a *MySQL* database. By Sinisa Milivojevic, . importsql.txt (http://www.tcx.se/Contrib/importsql.txt) A script that does the exact reverse of `exportsql.txt'. That is, it imports data from *MySQL* into an Access database via ODBC. This is very handy when combined with exportSQL, since it lets you use Access for all DB design and administration, and synchronize with your actual *MySQL* server either way. Free of charge. See `http://www.netdive.com/freebies/importsql/' for any updates. Created by Laurent Bossavit of NetDIVE. *Note*: Doesn't work with Access2 ! jms130b.zip (http://www.tcx.se/Contrib/jms130b.zip) JDBC driver for *MySQL*. Also contains a command line client and other examples. This driver is now rather old and one of the other drivers is recommended. By Xiaokun Kelvin ZHU and GWE Technologies. twz1jdbcForMysql-1.0.3-GA.tar.gz (http://www.tcx.se/Contrib/twz1jdbcForMysql-1.0.3-GA.tar.gz) New JDBC driver for *MySQL*. This is a production release and is actively developed. By Terrence W. Zellers, . You can always find the newest driver at `http://www.voicenet.com/~zellert/tjFM'. mod_auth_mysql-2.20.tar.gz (http://www.tcx.se/Contrib/mod_auth_mysql-2.20.tar.gz) Apache authentication module for *MySQL*. By Zeev Suraski, . *Please* register this module at: `http://bourbon.netvision.net.il/mysql/mod_auth_mysql/register.html'. The registering information is only used for statistical purposes and will encourage further development of this module! mod_log_mysql-1.05.tar.gz (http://www.tcx.se/Contrib/mod_log_mysql-1.05.tar.gz) *MySQL* logging module for Apache. By Zeev Suraski, . mrtg-mysql-1.0.tar.gz (http://www.tcx.se/Contrib/mrtg-mysql-1.0.tar.gz) *MySQL* status plotting with MRTG, by Luuk de Boer, . mysqladmin-atif-1.0.tar.gz (http://www.tcx.se/Contrib/mysqladmin-atif-1.0.tar.gz) WWW *MySQL* administrator for the `user,' `db' and `host' tables. By Tim Sailer, modified by Atif Ghaffar . mysqltcl-1.53.tar.gz (http://www.tcx.se/Contrib/mysqltcl-1.53.tar.gz) Tcl interface for *MySQL*. Based on `msqltcl-1.50.tar.gz'. Updated by Tobias Ritzau, . MySQLmodule-1.4.tar.gz (http://www.tcx.se/Contrib/MySQLmodule-1.4.tar.gz) Python interface for *MySQL*. By Joseph Skinner, . mypasswd-2.0.tar.gz (http://www.tcx.se/Contrib/mypasswd-2.0.tar.gz) Extra for `mod_auth_mysql'. This is a little tool that allows you to add/change user records storing group and/or password entries in *MySQL* tables. By Harry Brueckner, . mysql-c++-0.02.tar.gz (http://www.tcx.se/Contrib/mysql-c++-0.02.tar.gz) *MySQL* C++ wrapper library. By Roland Haenel, . C++ API (http://sunsite.unc.edu/kevina/mysql++/) *MySQL* C++ API; More than just a wrapper library. By . mysql-passwd.README (http://www.tcx.se/Contrib/mysql-passwd.README) mysql-passwd-1.2.tar.gz (http://www.tcx.se/Contrib/mysql-passwd-1.2.tar.gz) Extra for `mod_auth_mysql'. This is a two-part system for use with `mod_auth_mysql'. mysql_watchdog.pl (http://www.tcx.se/Contrib/mysql_watchdog.pl) Monitor the *MySQL* daemon for possible lockups. By Yermo Lamers, . mysql-webadmin-1.0a8-rz.tar.gz (http://www.tcx.se/Contrib/mysql-webadmin-1.0a8-rz.tar.gz) A tool written in PHP-FI to administrate *MySQL* databases remotely over the web within a Web-Browser. By Peter Kuppelwieser, . Updated by Wim Bonis, bonis@kiss.de. Not maintained anymore! phpMyAdmin_1.1.0.tar.gz (http://www.tcx.se/Contrib/phpMyAdmin_1.1.0.tar.gz) phpMyAdmin home page (http://www.htmlwizard.net/phpMyAdmin/) A PHP3 tool in the spirit of mysql-webadmin, by Tobias Ratschiller, tobias@dnet.it mysqladm.tar.gz (http://www.tcx.se/Contrib/mysqladm.tar.gz) *MySQL* Web Database Administration written in Perl. By Tim Sailer. mysqladm-2.tar.gz (http://www.tcx.se/Contrib/mysqladm-2.tar.gz) Updated version of `mysqladm.tar.gz', by High Tide. nsapi_auth_mysql.tar (http://www.tcx.se/Contrib/nsapi_auth_mysql.tar) Netscape Web Server API (NSAPI) functions to authenticate (BASIC) users against *MySQL* tables. By Yuan John Jiang. mysqlwinadmn.zip (http://www.tcx.se/Contrib/mysqlwinadmn.zip) Win32 GUI (binary only) to administrate a database, by David B. Mansel, . pam_mysql.tar.gz (http://www.tcx.se/Contrib/pam_mysql.tar.gz) This module authenticates users via `pam', using *MySQL*. pike-mysql-1.4.tar.gz (http://www.tcx.se/Contrib/pike-mysql-1.4.tar.gz) *MySQL* module for pike. For use with the Roxen web server. radius-0.3.tar.gz (http://www.tcx.se/Contrib/radius-0.3.tar.gz) Patches for `radiusd' to make it support *MySQL*. By Wim Bonis, . qmail-1.03-mysql-0.3.2.patch.gz (http://www.tcx.se/Contrib/qmail-1.03-mysql-0.3.2.patch.gz) checkpassword-0.76-mysql-0.3.2.patch.gz (http://www.tcx.se/Contrib/checkpassword-0.76-mysql-0.3.2.patch.gz) MySQL authentication patch for QMAIL and checkpassword. These are useful for management user(mail,pop account) by *MySQL*. By jradius-diff.gz (http://www.tcx.se/Contrib/jradius-diff.gz) *MySQL* support for Livingston's Radius 2.01. Authentication and Accounting. By Jose de Leon, sqlscreens-0.4.1.tar.gz (http://www.tcx.se/Contrib/sqlscreens-0.4.1.tar.gz) TCL/TK code to generate database screens. By Jean-Francois Dockes. squile.tar.gz (http://www.tcx.se/Contrib/squile.tar.gz) Module for `guile' that allows `guile' to interact with SQL databases. By Hal Roberts. mm.mysql.jdbc-0.9d.tar.gz (http://www.tcx.se/Contrib/mm.mysql.jdbc-0.9d.tar.gz) Another new java JDBC driver. By Mark Matthews, . UdmSearch-1.9.tar.gz (http://www.tcx.se/Contrib/UdmSearch-1.9.tar.gz) A *MySQL*- and PHP- based search engine over http. By Alexander I. Barkov . useradm.tar.gz (http://www.tcx.se/Contrib/useradm.tar.gz) *MySQL* administrator in PHP. By Ofni Thomas . wmtcl.doc (http://www.tcx.se/Contrib/wmtcl.doc) wmtcl.lex (http://www.tcx.se/Contrib/wmtcl.lex) With this you can write HTML files with inclusions of TCL code. By . wuftpd-2.4.2b12+mysql_support.tar.gz (http://www.tcx.se/Contrib/wuftpd-2.4.2b12+mysql_support.tar.gz) Patches to add logging to *MySQL* for WU-ftpd. By Zeev Suraski, . wuftpd-2.4.2.18+mysql_support.2.tar.gz (http://www.tcx.se/Contrib/wuftpd-2.4.2.18+mysql_support.2.tar.gz) Update to the above by www-sql-0.5.7.lsm (http://www.tcx.se/Contrib/www-sql-0.5.7.lsm) www-sql-0.5.3.md5 (http://www.tcx.se/Contrib/www-sql-0.5.3.md5) www-sql-0.5.7.tar.gz (http://www.tcx.se/Contrib/www-sql-0.5.7.tar.gz) A CGI program that parses an HTML file containing special tags, parses them and inserts data from a *MySQL* database. xmysql-1.9.tar.gz (http://www.tcx.se/Contrib/xmysql-1.9.tar.gz) xmysql home page (http://web.wt.net/~dblhack) A front end to the *MySQL* database engine. It allows for simple queries and table maintenance, as well as batch queries. By Rick Mehalick, . Requires xforms 0.88 (http://bragg.phys.uwm.edu/xforms) to work. xmysqladmin-1.0.tar.gz (http://www.tcx.se/Contrib/xmysqladmin-1.0.tar.gz) A front end to the *MySQL* database engine. It allows reloads, status check, process control, isamchk, grant/revoke privileges, creating databases, dropping databases, create, alter, browse and drop tables. Originally by Gilbert Therrien, but now in public domain and supported by TcX. Contributors to *MySQL* *********************** Contributors to the *MySQL* distribution are listed below, in somewhat random order: Michael (Monty) Widenius Has written the following parts of *MySQL*: * All the main code in `mysqld'. * New functions for the string library. * Most of the `mysys' library. * The `NISAM' library (A B-tree index file handler with index compression and different record formats). * The `heap' library. A memory table system with our superior full dynamic hashing. In use since 1981 and published around 1984. * The `replace' program (look into it, it's COOL!). * *MyODBC*, the ODBC driver for Windows95. * Fixing bugs in MIT-pthreads to get it to work for *MySQL*. And also Unireg, a curses-based application tool with many utilities. * Porting of `mSQL' tools like `msqlperl', `DBD'/`DBI' and `DB2mysql'. * Most parts of crash-me and the *MySQL* benchmarks. David Axmark * Coordinator and main writer for the *Reference Manual*, including enhancements to `texi2html'. Also automatic website updating from this manual. * Autoconf, Automake and `libtool' support. * The licensing stuff. * Parts of all the text files. (Nowadays only the `README' is left. The rest ended up in the manual.) * Our Mail master. * Lots of testing of new features. * Our in-house "free" software lawyer. * Mailing list maintainer (who never has the time to do it right...) * Our original portability code (more than 10 years old now). Nowadays only some parts of `mysys' are left. * Someone for Monty to call in the middle of the night when he just got that new feature to work. :-) Paul DuBois Help with making the Reference Manual correct and understandable. Gianmassimo Vigazzola or The initial port to Win32/NT. Kim Aldale Rewriting Monty's and David's attempts at English into English. Allan Larsson (The BOSS at TcX) For all the time he has allowed Monty to spend on this "maybe useful" tool (*MySQL*). Dedicated user (and bug finder) of Unireg & *MySQL*. Per Eric Olsson For more or less constructive criticism and real testing of the dynamic record format. Irena Pancirov Win32 port with Borland compiler. David J. Hughes For the effort to make a shareware SQL database. We at TcX started with `mSQL', but found that it couldn't satisfy our purposes so instead we wrote a SQL interface to our application builder Unireg. `mysqladmin' and `mysql' are programs that were largely influenced by their `mSQL' counterparts. We have put a lot of effort into making the *MySQL* syntax a superset of `mSQL'. Many of the API's ideas are borrowed from `mSQL' to make it easy to port free `mSQL' programs to *MySQL*. *MySQL* doesn't contain any code from `mSQL'. Two files in the distribution (`client/insert_test.c' and `client/select_test.c') are based on the corresponding (non-copyrighted) files in the `mSQL' distribution, but are modified as examples showing the changes necessary to convert code from `mSQL' to *MySQL*. (`mSQL' is copyrighted David J. Hughes.) Fred Fish For his excellent C debugging and trace library. Monty has made a number of smaller improvements to the library (speed and additional options). Richard A. O'Keefe For his public domain string library. Henry Spencer For his regex library, used in `WHERE column REGEXP regexp'. Free Software Foundation From whom we got an excellent compiler (`gcc'), the `libc' library (from which we have borrowed `strto.c' to get some code working in Linux) and the `readline' library (for the `mysql' client). Free Software Foundation & The XEmacs development team For a really great editor/environment used by almost everybody at TcX/detron. Igor Romanenko `mysqldump' (previously `msqldump', but ported and enhanced by Monty). Tim Bunce, Alligator Descartes For the `DBD' (Perl) interface. Andreas Koenig For the Perl interface to *MySQL*. Eugene Chan For porting PHP to *MySQL*. Michael J. Miller Jr. For the growing *MySQL* user manual. And a lot of spelling/language fixes for the FAQ. Giovanni Maruzzelli For porting iODBC (Unix ODBC). Chris Provenzano Portable user level pthreads. From the copyright: This product includes software developed by Chris Provenzano, the University of California, Berkeley, and contributors. We are currently using version 1_60_beta6 patched by Monty (see `mit-pthreads/Changes-mysql'). Xavier Leroy The author of LinuxThreads (used by *MySQL* on Linux). Zarko Mocnik Sorting for Slovenian language and the `cset.tar.gz' module that makes it easier to add other character sets. "TAMITO" The `_MB' character set macros and the ujis and sjis character sets. Yves Carlier `mysqlaccess', a program to show the access rights for a user. Rhys Jones (And GWE Technologies Limited) For the JDBC, a module to extract data from *MySQL* with a Java client. Dr Xiaokun Kelvin ZHU Further development of the JDBC driver and other *MySQL*-related Java tools. James Cooper For setting up a searchable mailing list archive at his site. Rick Mehalick For `xmysql', a graphical X client for *MySQL*. Doug Sisk For providing RPM packages of *MySQL* for RedHat Linux. Diemand Alexander V. For providing RPM packages of *MySQL* for RedHat Linux/Alpha. Antoni Pamies Olive For providing RPM versions of a lot of *MySQL* clients for Intel and Sparc. Jay Bloodworth For providing RPM versions for *MySQL* 3.21 versions. Jochen Wiedmann For maintaining the Perl `DBD::mysql' module. Therrien Gilbert , Jean-Marc Pouyot French error messages. Petr snajdr, Czech error messages. Jaroslaw Lewandowski Polish error messages. Miguel Angel Fernandez Roiz Spanish error messages. Roy-Magne Mo Norwegian error messages and testing of 3.21.#. Timur I. Bakeyev Russian error messages. brenno@dewinter.com Italian error messages. Dirk Munzinger German error messages. Billik Stefan Slovak error messages. David Sacerdote Ideas for secure checking of DNS hostnames. Wei-Jou Chen Some support for Chinese(BIG5) characters. Zeev Suraski `FROM_UNIXTIME()' time formatting, `ENCRYPT()' functions, and `bison' adviser. Active mailing list member. Luuk de Boer Ported (and extended) the benchmark suite to `DBI'/`DBD'. Have been of great help with `crash-me' and running benchmarks. Some new date functions. The mysql_setpermissions script. Jay Flaherty Big parts of the Perl `DBI'/`DBD' section in the manual. Paul Southworth , Ray Loyzaga Proof-reading of the Reference Manual. Alexis Mikhailov User definable functions (UDFs); `CREATE FUNCTION' and `DROP FUNCTION'. Ross Wakelin Help to set up InstallShield for MySQL-Win32. Jethro Wright III The `libmysql.dll' library. James Pereria Mysqlmanager, a Win32 GUI tool for administrating *MySQL*. Curt Sampson Porting of MIT-pthreads to NetBSD/Alpha and NetBSD 1.3/i386. Sinisa Milivojevic Compression (with `zlib') to the client/server protocol. Perfect hashing for the lexical analyzer phase. Antony T. Curtis Porting of *MySQL* to OS/2. Other contributors, bugfinders and testers: James H. Thompson, Maurizio Menghini, Wojciech Tryc, Luca Berra, Zarko Mocnik, Wim Bonis, Elmar Haneke, , , , Ted Deppner , Mike Simons, Jaakko Hyv"atti. And lots of bug report/patches from the folks on the mailing list. And a big tribute to those that help us answer questions on the `mysql@tcx.se' mailing list: Daniel Koch IRIX setup. Luuk de Boer Benchmark questions. Tim Sailer `DBD-mysql' questions. Boyd Lynn Gerber SCO related questions. Richard Mehalick `xmysql'-releated questions and basic installation questions. Zeev Suraski Apache module configuration questions (log & auth), PHP-related questions, SQL syntax related questions and other general questions. Francesc Guasch General questions. Jonathan J Smith Questions pertaining to OS-specifics with Linux, SQL syntax, and other things that might be needing some work. David Sklar Using *MySQL* from PHP and Perl. Alistair MacDonald Not yet specified, but is flexible and can handle Linux and maybe HP-UX. Will try to get user to use `mysqlbug'. John Lyon Questions about installing *MySQL* on Linux systems, using either `.rpm' files, or compiling from source. Lorvid Ltd. Simple billing/license/support/copyright issues. Patrick Sherrill ODBC and VisualC++ interface questions. Randy Harmon `DBD', Linux, some SQL syntax questions. *MySQL* change history ********************** Changes in release 3.22.x (Beta version) ======================================== The 3.22 version has faster and safer connect code and a lot of new nice enhancements. The reason for not including these changes in the 3.21 version is mainly that we are trying to avoid big changes to 3.21 to keep it as stable as possible. As there aren't really any MAJOR changes, upgrading to 3.22 should be very easy and painless. 3.22 should also be used with the new `DBD-mysql' (1.2000) driver that can use the new connect protocol! Note that we tend to update the manual at the same time we implement new things to *MySQL*. If you find a version listed below that you can't find on the *MySQL* download page (http://www.tcx.se/download.html), this means that the version has not yet been released! Note that we tend to update the manual at the same time we implement new things to *MySQL*. If you find a version listed below that you can't find on the *MySQL* download page (http://www.tcx.se/download.html), this means that the version has not yet been released! Changes in release 3.22.14 -------------------------- * Allow empty arguments to `mysqld' to make it easier to start it from shell scripts. * Setting a `TIMESTAMP' column to `NULL' didn't record the timestamp value in the update log. * Fixed lock handler bug when one did: `INSERT INTO TABLE ... SELECT ... GROUP BY.' * Added a patch for `localtime_r()' on Win32 that it will not crash anymore if your date is > 2039, but instead it will return a time of all zero. * `UDF' function names are not longer case sensitive. * Added escape of `^Z' (ASCII 26) to `\Z 'as `^Z' doesn't work with pipes on Win32. * mysql_fix_privileges adds a new column to the `mysql.func' to support aggregate UDF functions in future `MySQL' releases. Changes in release 3.22.13 -------------------------- * Saving NOW(), CURDATE() or CURTIME() directly in a column didn't work. * `SELECT COUNT(*) ... LEFT JOIN ...' didn't work with no `WHERE' part. * Updated config.guess to allow *MySQL* to configure on UnixWare 7.0.x * Changed the implementation of `pthread_cond()' on the Win32 version. `get_lock()' now correctly times out on Win32! Changes in release 3.22.12 -------------------------- * Fixed problem when using `DATE_ADD()' and `DATE_SUB()' in a `WHERE' clause. * You can now set the password for a user with the `GRANT ... TO user IDENTIFIED BY 'password'' syntax. * Fixed bug in `GRANT' checking with `SELECT' on many tables. * Added missing file `mysql_fix_privilege_tables' to the RPM distribution. This is not run by default since it relies on the client package. * Added option `SQL_SMALL_RESULT' to `SELECT' to force use of fast temporary tables when you know that the result set will be small. * Allow use of negative real numbers without a decimal point. * Day number is now adjusted to max days in month if the resulting month after `DATE_ADD'/`DATE_SUB()' doesn't have enough days. * Fix that `GRANT' compares columns in case-insensitive fashion. * Fixed a bug in `sql_list.h' that made `ALTER TABLE' dump core in some contexts. * The hostname in `user@hostname' can now include `.' and `-' without quotes in the context of the `GRANT', `REVOKE' and `SET PASSWORD FOR ...' statements. * Fix for `isamchk' for tables which need big temporary files. Changes in release 3.22.11 -------------------------- * *IMPORTANT*: You must run the `mysql_fix_privilege_tables' script when you upgrade to this version! This is needed because of the new `GRANT' system. If you don't do this, you will get `Access denied' when you try to use `ALTER TABLE', `CREATE INDEX' or `DROP INDEX'. * `GRANT' to allow/deny users table and column access. * Changed `USER()' to return `user@host' * Changed the syntax for how to set `PASSWORD' for another user. * New command `FLUSH STATUS' that sets most status variables to zero. * New status variables: `aborted_threads', `aborted_connects'. * New option variable: `connection_timeout'. * Added support for Thai sorting (by Pruet Boonma ). * Slovak and japanese error messages. * Configuration and portability fixes. * Added option `SET SQL_WARNINGS=1' to get a warning count also for simple inserts. * *MySQL* now uses `SIGTERM' instead of `SIGQUIT' with shutdown to work better on FreeBSD. * Added option `\G' (print vertically) to `mysql'. * `SELECT HIGH_PRIORITY' ... killed `mysqld'. * `IS NULL' on a `AUTO_INCREMENT' column in a `LEFT JOIN' didn't work as expected. * New function `MAKE_SET'. Changes in release 3.22.10 -------------------------- * `mysql_install_db' no longer starts the *MySQL* server! You should start `mysqld' with `safe_mysqld' after installing it! The *MySQL* RPM will however start the server as before. * Added `--bootstrap' option to `mysqld' and recoded `mysql_install_db' to use it. This will make it easier to install *MySQL* with RPMs. * Changed `+', `-' (sign and minus), `*', `/', `%', `ABS()' and `MOD()' to be `BIGINT' aware (64-bit safe). * Fixed a bug in `ALTER TABLE' that caused `mysqld' to crash. * *MySQL* now always reports the conflicting key values when a duplicate key entry occurs. (Before this was only reported for `INSERT'). * New syntax: `INSERT INTO tbl_name SET col_name=value,col_name=value...' * Most errors in the `.err' log are now prefixed with a time stamp. * Added option `MYSQL_INIT_COMMAND' to `mysql_options()' to make a query on connect or reconnect. * Added option `MYSQL_READ_DEFAULT_FILE' and `MYSQL_READ_DEFAULT_GROUP' to `mysql_options()' to read the following parameters from the *MySQL* option files: port, socket, compress, password, pipe, timeout, user, init-command, host and database. * Added `maybe_null' to the UDF structure. * Added option `IGNORE' to `INSERT' statemants with many rows. * Fixed some problems with sorting of the koi8 character sets; Users of koi8 *MUST* run `isamchk -rq' on each table that has an index on a `CHAR' or `VARCHAR' column. * New script `mysql_setpermission', by Luuk de Boer, allows one to easily create new users with permissions for specific databases. * Allow use of hexadecimal strings (0x...) when specifying a constant string (like in the column separators with `LOAD DATA INFILE'). * Ported to OS/2 (thanks to Antony T. Curtis ). * Added more variables to `SHOW STATUS' and changed format of output to be like `SHOW VARIABLES'. * Added `extended-status' command to `mysqladmin' which will show the new status variables. Changes in release 3.22.9 ------------------------- * `SET SQL_LOG_UPDATE=0' caused a lockup of the server. * New SQL command: `FLUSH [ TABLES | HOSTS | LOGS | PRIVILEGES ] [, ...]' * New SQL command: `KILL' thread_id * Added casts and changed include files to make *MySQL* easier to compile on AIX and DEC OSF1 4.x * Fixed conversion problem when using `ALTER TABLE' from a `INT' to a short `CHAR()' column. * Added `SELECT HIGH_PRIORITY'; This will get a lock for the `SELECT' even if there is a thread waiting for another `SELECT' to get a `WRITE LOCK'. * Moved wild_compare to string class to be able to use `LIKE' on `BLOB'/`TEXT' columns with \0. * Added `ESCAPE' option to `LIKE' * Added a lot more output to `mysqladmin debug'. * You can now start `mysqld' on Win32 with the `--flush' option. This will flush all tables to disk after each update. This makes things much safer on NT/Win98 but also *MUCH* slower. Changes in release 3.22.8 ------------------------- * Czech character sets should now work much better. You must also install `ftp://www.tcx.se/pub/mysql/Downloads/Patches/czech-3.22.8-patch'. This patch should also be installed if you are using a character set with uses `my_strcoll()'! The patch should always be safe to install (for any system), but as this patch changes ISAM internals it's not yet in the default distribution. * `DATE_ADD()' and `DATE_SUB()' didn't work with group functions. * `mysql' will now also try to reconnect on `USE DATABASE' commands. * Fix problem with `ORDER BY' and `LEFT JOIN' and `const' tables. * Fixed problem with `ORDER BY' if the first `ORDER BY' column was a key and the rest of the `ORDER BY' columns wasn't part of the key. * Fixed a big problem with `OPTIMIZE TABLE'. * MySQL clients on NT will now by default first try to connect with named pipes and after this with TCP/IP. * Fixed a problem with `DROP TABLE' and `mysqladmin shutdown' on Win32 (a fatal bug from 3.22.6). * Fixed problems with `TIME columns' and negative strings. * Added an extra thread signal loop on shutdown to avoid some error messages from the client. * *MySQL* now uses the next available number as extension for the update log file. * Added patches for UNIXWARE 7. Changes in release 3.22.7 ------------------------- * You can now use the `/*! ... */' syntax to hide *MySQL*-specific keywords when you write portable code. *MySQL* will parse the code inside the comments as if the surrounding `/*!' and `*/' comment characters didn't exist. * `OPTIMIZE TABLE tbl_name' can now be used to reclaim disk space after many deletes. Currently, this uses `ALTER TABLE' to re-generate the table, but in the future it will use an integrated `isamchk' for more speed. * Upgraded `libtool' to get the configure more portable. * Fixed slow `UPDATE' and `DELETE' operations when using `DATETIME' or `DATE' keys. * Changed optimizer to make it better at deciding when to do a full join and when using keys. * You can now use `mysqladmin proc' to display information about your own threads. Only users with the *Process_priv* privilege can get information about all threads. * Added handling of formats `YYMMDD', `YYYYMMDD', `YYMMDDHHMMSS' for numbers when using `DATETIME' and `TIMESTAMP' types. (Formerly these formats only worked with strings.) * Added connect option `CLIENT_IGNORE_SPACE' to allow use of spaces after function names and before `(' (Powerbuilder requires this). This will make all function names reserved words. * Added the `--log-long-format' option to `mysqld' to enable timestamps and INSERT_ID's in the update log. * Added `--where' option to `mysqldump' (patch by Jim Faucette). * The lexical analyzer now uses "perfect hashing" for faster parsing of SQL statements. Changes in release 3.22.6 ------------------------- * Faster `mysqldump'. * For the `LOAD DATA INFILE' statement, you can now use the new `LOCAL' keyword to read the file from the client. `mysqlimport' will automatically use `LOCAL' when importing with the TCP/IP protocol. * Fixed small optimize problem when updating keys. * Changed makefiles to support shared libraries. * MySQL-NT can now use named pipes, which means that you can now use MySQL-NT without having to install TCP/IP. Changes in release 3.22.5 ------------------------- * All table lock handing is changed to avoid some very subtle deadlocks when using `DROP TABLE', `ALTER TABLE', `DELETE FROM TABLE' and `mysqladmin flush-tables' under heavy usage. Changed locking code to get better handling of locks of different types. * Updated `DBI' to 1.00 and `DBD' to 1.2.0. * Added a check that the error message file contains error messages suitable for the current version of `mysqld'. (To avoid errors if you accidentally try to use an old error message file.) * All count structures in the client (affected_rows, insert_id...) are now of type `BIGINT' to allow use of 64-bit values. This required a minor change in the *MySQL* protocol which should affect only old clients when using tables with `AUTO_INCREMENT' values > 24M. * The return type of `mysql_fetch_lengths()' has changed from `uint *' to `ulong *'. This may give a warning for old clients but should work on most machines. * Change `mysys' and `dbug' libraries to allocate all thread variables in one struct. This makes it easier to make a threaded `libmysql.dll' library. * Use the result from `gethostname()' (instead of `uname()') when constructing `.pid' file names. * New better compressed server/client protocol. * `COUNT()', `STD()' and `AVG()' are extended to handle more than 4G rows. * You can now store values in the range `-838:59:59' <= x <= `838:59:59' in a `TIME' column. * *WARNING: INCOMPATIBLE CHANGE!!* If you set a `TIME' column to too short a value, *MySQL* now assumes the value is given as: `[[[D ]HH:]MM:]SS' instead of `HH[:MM[:SS]]'. * `TIME_TO_SEC()' and `SEC_TO_TIME()' can now handle negative times and hours up to 32767. * Added new option `SET OPTION SQL_LOG_UPDATE={0|1}' to allow users with the *process* privilege to bypass the update log. (Modified patch from Sergey A Mukhin .) * Fixed fatal bug in `LPAD()'. * Initialize line buffer in `mysql.cc' to make `BLOB' reading from pipes safer. * Added `-O max_connect_errors=#' option to `mysqld'. Connect errors are now reset for each correct connection. * Increased the default value of `max_allowed_packet' to 1M in `mysqld'. * Added `--low-priority-updates' option to `mysqld', to give `UPDATE' operations lower priority than retrievals. You can now use `{INSERT | REPLACE | UPDATE | DELETE} LOW_PRIORITY ...' You can also use `SET OPTION LOW_PRIORITY_UPDATES={0|1}' to change the priority for one thread. One side effect is that `LOW_PRIORITY' is now a reserved word. :( * Add support for `INSERT INTO table ... VALUES(...),(...),(...)', to allow inserting multiple rows with a single statement. * `INSERT INTO tbl_name' is now also cached when used with `LOCK TABLES'. (Previously only `INSERT ... SELECT' and `LOAD DATA INFILE' were cached.) * Allow `GROUP BY' functions with `HAVING': mysql> SELECT col FROM table GROUP BY col HAVING COUNT(*)>0; * `mysqld' will now ignore trailing `;' characters in queries. This is to make it easier to migrate from some other SQL servers that require the trailing `;'. * Fix for corrupted fixed-format output generated by `SELECT INTO OUTFILE'. * *WARNING: INCOMPATIBLE CHANGE!!* Added Oracle `GREATEST()' and `LEAST()' functions. You must now use these instead of the `MAX()' and `MIN()' functions to get the largest/smallest value from a list of values. These can now handle `REAL', `BIGINT' and string (`CHAR' or `VARCHAR') values. * *WARNING: INCOMPATIBLE CHANGE!!* `DAYOFWEEK()' had offset 0 for Sunday. Changed the offset to 1. * Give an error for queries that mix `GROUP BY' columns and fields when there is no `GROUP BY' specification. * Added `--vertical' option to `mysql', for printing results in vertical mode. * Index-only optimization; some queries are now resolved using only indexes. Until *MySQL* 4.0, this works only for numeric columns. *Note *MySQL* indexes: MySQL indexes. * Lots of new benchmarks. * A new C API chapter and lots of other improvements in the manual. Changes in release 3.22.4 ------------------------- * Added `--tmpdir' option to `mysqld', for specifying the location of the temporary file directory. * *MySQL* now automatically changes a query from an ODBC client: SELECT ... FROM table WHERE auto_increment_column IS NULL to: SELECT ... FROM table WHERE auto_increment_column == LAST_INSERT_ID() This allows some ODBC programs (Delphi, Access) to retrieve the newly inserted row to fetch the `AUTO_INCREMENT' id. * `DROP TABLE' now waits for all users to free a table before deleting it. * Fixed small memory leak in the new connect protocol. * New functions `BIN()', `HEX()' and `CONV()' for converting between different number bases. * Added function `SUBSTRING()' with 2 arguments. * If you created a table with a record length smaller than 5, you couldn't delete rows from the table. * Added optimization to remove const reference tables from `ORDER BY' and `GROUP BY'. * `mysqld' now automatically disables system locking on Linux and Win32, and for systems that use MIT-pthreads. You can force the use of locking with the `--enable-locking' option. * Added `--console' option to `mysqld', to force a console window (for error messages) when using Win32. * Fixed table locks for Win32. * Allow `$' in identifiers. * Changed name of user-specific configuration file from `my.cnf' to `.my.cnf' (Unix only). * Added `DATE_ADD()' and `DATE_SUB()' functions. Changes in release 3.22.3 ------------------------- * Fixed a lock problem (bug in *MySQL* 3.22.1) when closing temporary tables. * Added missing `mysql_ping()' to the client library. * Added `--compress' option to all *MySQL* clients. * Changed `byte' to `char' in `mysql.h' and `mysql_com.h'. Changes in release 3.22.2 ------------------------- * Searching on multiple constant keys that matched > 30% of the rows didn't always use the best possible key. * New functions `<<', `>>', `RPAD()' and `LPAD()'. * You can now save default options (like passwords) in a configuration file (`my.cnf'). * Lots of small changes to get `ORDER BY' to work when no records are found when using fields that are not in `GROUP BY' (MySQL extension). * Added `--chroot' option to `mysqld', to start `mysqld' in a chroot environment (by Nikki Chumakov ). * Trailing space is now ignored when comparing case-sensitive strings; this should fix some problems with ODBC and flag 512! * Fixed a core-dump bug in the range optimizer. * Added `--one-thread' option to `mysqld', for debugging with LinuxThreads (or `glibc'). (This replaces the `-T32' flag) * Added `DROP TABLE IF EXISTS' to prevent an error from occurring if the table doesn't exist. * `IF' and `EXISTS' are now reserved words (they would have to be sooner or later). * Added lots of new options to `mysqldump'. * Server error messages are now in `mysqld_error.h'. * The server/client protocol now supports compression. * All bug fixes from *MySQL* 3.21.32. Changes in release 3.22.1 ------------------------- * Added new C API function `mysql_ping()'. * Added new API functions `mysql_init()' and `mysql_options()'. You now MUST call `mysql_init()' before you call `mysql_real_connect()'. You don't have to call `mysql_init()' if you only use `mysql_connect()'. * Added `mysql_options(...,MYSQL_OPT_CONNECT_TIMEOUT,...)' so you can set a timeout for connecting to a server. * Added `--timeout' option to `mysqladmin', as a test of `mysql_options()'. * Added `AFTER column' and `FIRST' options to `ALTER TABLE ... ADD columns'. This makes it possible to add a new column at some specific location within a row in an existing table. * `WEEK()' now takes an optional argument to allow handling of weeks when the week starts on Monday (some European countries). By default, `WEEK()' assumes the week starts on Sunday. * `TIME' columns weren't stored properly (bug in *MySQL* 3.22.0). * `UPDATE' now returns information about how many rows were matched and updated, and how many "warnings" occurred when doing the update. * Fixed incorrect result from `FORMAT(-100,2)'. * `ENUM' and `SET' columns were compared in binary (case-sensitive) fashion; changed to be case insensitive. Changes in release 3.22.0 ------------------------- * New (backward compatible) connect protocol that allows you to specify the database to use when connecting, to get much faster connections to a specific database. The `mysql_real_connect()' call is changed to: mysql_real_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd, const char *db, uint port, const char *unix_socket, uint client_flag) * Each connection is handled by its own thread, rather than by the master `accept()' thread. This fixes permanently the telnet bug that was a topic on the mail list some time ago. * All TCP/IP connections are now checked with backward resolution of the hostname to get better security. `mysqld' now has a local hostname resolver cache so connections should actually be faster than before, even with this feature. * A site automatically will be blocked from future connections if someone repeatedly connects with an "improper header" (like when one uses telnet). * You can now refer to tables in different databases with references of the form `tbl_name@db_name' or `db_name.tbl_name'. This makes it possible to give a user read access to some tables and write access to others simply by keeping them in different databases! * Added `--user' option to `mysqld', to allow it to run as another Unix user (if it is started as the Unix `root' user). * Added caching of users and access rights (for faster access rights checking) * Normal users (not anonymous ones) can change their password with `mysqladmin password 'new_password''. This uses encrypted passwords that are not logged in the normal *MySQL* log! * All important string functions are now coded in assembler for x86 Linux machines. This gives a speedup of 10% in many cases. * For tables that have many columns, the column names are now hashed for much faster column name lookup (this will speed up some benchmark tests a lot!) * Some benchmarks are changed to get better individual timing. (Some loops were so short that a specific test took < 2 seconds. The loops have been changed to take about 20 seconds to make it easier to compare different databases. A test that took 1-2 seconds before now takes 11-24 seconds, which is much better) * Re-arranged `SELECT' code to handle some very specific queries involving group functions (like `COUNT(*)') without a `GROUP BY' but with `HAVING'. The following now works: mysql> SELECT count(*) as C FROM table HAVING C > 1; * Changed the protocol for field functions to be faster and avoid some calls to `malloc()'. * Added `-T32' option to `mysqld', for running all queries under the main thread. This makes it possible to debug `mysqld' under Linux with `gdb'! * Added optimization of `not_null_column IS NULL' (needed for some Access queries). * Allow `STRAIGHT_JOIN' to be used between two tables to force the optimizer to join them in a specific order. * String functions now return `VARCHAR' rather than `CHAR' and the column type is now `VARCHAR' for fields saved as `VARCHAR'. This should make the *MyODBC* driver better, but may break some old *MySQL* clients that don't handle `FIELD_TYPE_VARCHAR' the same way as `FIELD_TYPE_CHAR'. * `CREATE INDEX' and `DROP INDEX' are now implemented through `ALTER TABLE'. `CREATE TABLE' is still the recommended (fast) way to create indexes. * Added `--set-variable' option `wait_timeout' to `mysqld'. * Added time column to `mysqladmin processlist' to show how long a query has taken or how long a thread has slept. * Added lots of new variables to `show variables' and some new to `show status'. * Added new type `YEAR'. `YEAR' is stored in 1 byte with allowable values of 0, and 1901 to 2155. * Added new `DATE' type that is stored in 3 bytes rather than 4 bytes. All new tables are created with the new date type if you don't use the `--old-protocol' option to `mysqld'. * Fixed bug in record caches; for some queries, you could get `Error from table handler: #' on some operating systems. * Added `--enable-assembler' option to `configure', for x86 machines (tested on Linux + `gcc'). This will enable assembler functions for the most important string functions for more speed! Changes in release 3.21.x ========================= Changes in release 3.21.33 -------------------------- * Fixed problem when sending `SIGHUP' to `mysqld'; `mysqld' core dumped when starting from boot on some systems. * Fixed problem with losing a little memory for some connections. * `DELETE FROM tbl_name' without a `WHERE' condition is now done the long way when you use `LOCK TABLES' or if the table is in use, to avoid race conditions. * `INSERT INTO TABLE (timestamp_column) VALUES (NULL);' didn't set timestamp. Changes in release 3.21.32 -------------------------- * Fixed some possible race conditions when doing many reopen/close on the same tables under heavy load! This can happen if you execute `mysqladmin refresh' often. This could in some very rare cases corrupt the header of the index file and cause error 126 or 138. * Fixed fatal bug in `refresh()' when running with the `--skip-locking' option. There was a "very small" time gap after a `mysqladmin refresh' when a table could be corrupted if one thread updated a table while another thread did `mysqladmin refresh' and another thread started a new update ont the same table before the first thread had finished. A refresh (or `--flush-tables') will now not return until all used tables are closed! * `SELECT DISTINCT' with a `WHERE' clause that didn't match any rows returned a row in some contexts (bug only in 3.21.31). * `GROUP BY' + `ORDER BY' returned one empty row when no rows where found. * Fixed a bug in the range optimizer that wrote `Use_count: Wrong count for ...' in the error log file. Changes in release 3.21.31 -------------------------- * Fixed a sign extension problem for the `TINYINT' type on IRIX. * Fixed problem with `LEFT("constant_string",function)'. * Fixed problem with `FIND_IN_SET()'. * `LEFT JOIN' core dumped if the second table is used with a constant `WHERE/ON' expression that uniquely identifies one record. * Fixed problems with `DATE_FORMAT()' and incorrect dates. `DATE_FORMAT()' now ignores `'%'' to make it possible to extend it more easily in the future. Changes in release 3.21.30 -------------------------- * `mysql' now returns an exit code > 0 if the query returned an error. * Saving of command line history to file in `mysql' client. By Tommy Larsen . * Fixed problem with empty lines that were ignored in `mysql.cc'. * Save the pid of the signal handler thread in the pid file instead of the pid of the main thread. * Added patch by to support Japanese characters SJIS and UJIS. * Changed `safe_mysqld' to redirect startup messages to `'hostname'.err' instead of `'hostname'.log' to reclaim file space on `mysqladmin refresh'. * `ENUM' always had the first entry as default value. * `ALTER TABLE' wrote two entries to the update log. * `sql_acc()' now closes the `mysql' grant tables after a reload to save table space and memory. * Changed `LOAD DATA' to use less memory with tables and `BLOB' columns. * Sorting on a function which made a division / 0 produced a wrong set in some cases. * Fixed `SELECT' problem with `LEFT()' when using the czech character set. * Fixed problem in `isamchk'; it couldn't repair a packed table in a very unusual case. * `SELECT' statements with `&' or `|' (bit functions) failed on columns with `NULL' values. * When comparing a field = field, where one of the fields was a part key, only the length of the part key was compared. Changes in release 3.21.29 -------------------------- * `LOCK TABLES' + `DELETE from tbl_name' never removed locks properly. * Fixed problem when grouping on an `OR' function. * Fixed permission problem with `umask()' and creating new databases. * Fixed permission problem on result file with `SELECT ... INTO OUTFILE ...' * Fixed problem in range optimizer (core dump) for a very complex query. * Fixed problem when using `MIN(integer)' or `MAX(integer)' in `GROUP BY'. * Fixed bug on Alpha when using integer keys. (Other keys worked on Alpha). * Fixed bug in `WEEK("XXXX-xx-01")'. Changes in release 3.21.28 -------------------------- * Fixed socket permission (clients couldn't connect to Unix socket on Linux). * Fixed bug in record caches; for some queries, you could get `Error from table handler: #' on some operating systems. Changes in release 3.21.27 -------------------------- * Added user level lock functions `GET_LOCK(string,timeout)', `RELEASE_LOCK(string)'. * Added `opened_tables' to `show status'. * Changed connect timeout to 3 seconds to make it somewhat harder for crackers to kill `mysqld' through telnet + TCP/IP. * Fixed bug in range optimizer when using `WHERE key_part_1 >= something AND key_part_2 <= something_else'. * Changed `configure' for detection of FreeBSD 3.0 9803xx and above * `WHERE' with string_column_key = constant_string didn't always find all rows if the column had many values differing only with characters of the same sort value (like e and 'e). * Strings keys looked up with 'ref' were not compared in case-sensitive fashion. * Added `umask()' to make log files non-readable for normal users. * Ignore users with old (8-byte) password on startup if not using `--old-protocol' option to `mysqld'. * `SELECT' which matched all key fields returned the values in the case of the matched values, not of the found values. (Minor problem.) Changes in release 3.21.26 -------------------------- * `FROM_DAYS(0)' now returns "0000-00-00". * In `DATE_FORMAT()', PM and AM were swapped for hours 00 and 12. * Extended the default maximum key size to 256. * Fixed bug when using `BLOB'/`TEXT' in `GROUP BY' with many tables. * An `ENUM' field that is not declared `NOT NULL' has `NULL' as the default value. (Previously, the default value was the first enumeration value.) * Fixed bug in the join optimizer code when using many part keys on the same key: `INDEX (Organization,Surname(35),Initials(35))'. * Added some tests to the table order optimizer to get some cases with `SELECT ... FROM many_tables' much faster. * Added a retry loop around `accept()' to possibly fix some problems on some Linux machines. Changes in release 3.21.25 -------------------------- * Changed `typedef 'string'' to `typedef 'my_string'' for better portability. * You can now kill threads that are waiting on a disk full condition. * Fixed some problems with UDF functions. * Added long options to `isamchk'. Try `isamchk --help'. * Fixed a bug when using 8 bytes long (alpha); `filesort()' didn't work. Affects `DISTINCT', `ORDER BY' and `GROUP BY' on 64-bit processors. Changes in release 3.21.24 -------------------------- * Dynamic loadable functions. Based on source from Alexis Mikhailov. * You couldn't delete from a table if no one had done a `SELECT' on the table. * Fixed problem with range optimizer with many `OR' operators on key parts inside each other. * Recoded `MIN()' and `MAX()' to work properly with strings and `HAVING'. * Changed default umask value for new files from `0664' to `0660'. * Fixed problem with `LEFT JOIN' and constant expressions in the `ON' part. * Added Italian error messages from . * `configure' now works better on OSF1 (tested on 4.0D). * Added hooks to allow `LIKE' optimization with international character support. * Upgraded `DBI' to 0.93. Changes in release 3.21.23 -------------------------- * The following symbols are now reserved words: `TIME', `DATE', `TIMESTAMP', `TEXT', `BIT', `ENUM', `NO', `ACTION', `CHECK', `YEAR', `MONTH', `DAY', `HOUR', `MINUTE', `SECOND', `STATUS', `VARIABLES'. * Setting a `TIMESTAMP' to `NULL' in `LOAD DATA INFILE ...' didn't set the current time for the `TIMESTAMP'. * Fix `BETWEEN' to recognize binary strings. Now `BETWEEN' is case sensitive. * Added `--skip-thread-priority' option to `mysqld', for systems where `mysqld''s thread scheduling doesn't work properly (BSDI 3.1). * Added ODBC functions `DAYNAME()' and `MONTHNAME()'. * Added function `TIME_FORMAT()'. This works like `DATE_FORMAT()', but takes a time string (`'HH:MM:DD'') as argument. * Fixed unlikely(?) key optimizer bug when using `OR's of key parts inside `AND's. * Added command `variables' to `mysqladmin'. * A lot of small changes to the binary releases. * Fixed a bug in the new protocol from *MySQL* 3.21.20. * Changed `ALTER TABLE' to work with Win32 (Win32 can't rename open files). Also fixed a couple of small bugs in the Win32 version. * All standard *MySQL* clients are now ported to MySQL-Win32. * *MySQL* can now be started as a service on NT. Changes in release 3.21.22 -------------------------- * Starting with this version, all *MySQL* distributions will be configured, compiled and tested with `crash-me' and the benchmarks on the following platforms: SunOS 5.6 sun4u, SunOS 5.5.1 sun4u, SunOS 4.14 sun4c, SunOS 5.6 i86pc, IRIX 6.3 mips5k, HP-UX 10.20 hppa, AIX 4.2.1 ppc, OSF1 V4.0 alpha, FreeBSD 2.2.2 i86pc and BSDI 3.1 i386. * Fix `COUNT(*)' problems when the `WHERE' clause didn't match any records. (Bug from 3.21.17.) * Removed that `NULL = NULL' is true. Now you must use `IS NULL' or `IS NOT NULL' to test whether or not a value is `NULL'. (This is according to ANSI SQL but may break old applications that are ported from `mSQL'.) You can get the old behavior by compiling with `-DmSQL_COMPLIANT'. * Fixed bug that core dumped when using many `LEFT OUTER JOIN' clauses. * Fixed bug in `ORDER BY' on string formula with possible `NULL' values. * Fixed problem in range optimizer when using <= on sub index. * Added functions `DAYOFYEAR()', `DAYOFMONTH()', `MONTH()', `YEAR()', `WEEK()', `QUARTER()', `HOUR()', `MINUTE()', `SECOND()' and `FIND_IN_SET()'. * Added command `SHOW VARIABLES'. * Added support of "long constant strings" from ANSI SQL: mysql> SELECT 'first ' 'second'; -> 'first second' * Upgraded mSQL-Mysql-modules to 1.1825. * Upgraded `mysqlaccess' to 2.02. * Fixed problem with Russian character set and `LIKE'. * Ported to OpenBSD 2.1. * New Dutch error messages. Changes in release 3.21.21a --------------------------- * Configure changes for some operating systems. Changes in release 3.21.21 -------------------------- * Fixed optimizer bug when using `WHERE data_field = date_field2 AND date_field2 = constant'. * Added command `SHOW STATUS'. * Removed `manual.ps' from the source distribution to make it smaller. Changes in release 3.21.20 -------------------------- * Changed the maximum table name and column name lengths from 32 to 64. * Aliases can now be of "any" length. * Fixed `mysqladmin stat' to return the right number of queries. * Changed protocol (downward compatible) to mark if a column has the `AUTO_INCREMENT' attribute or is a `TIMESTAMP'. This is needed for the new Java driver. * Added Hebrew sorting order by Zeev Suraski. * Solaris 2.6: Fixed `configure' bugs and increased maximum table size from 2G to 4G. Changes in release 3.21.19 -------------------------- * Upgraded `DBD' to 1823. This version implements `mysql_use_result' in `DBD-Mysql'. * Benchmarks updated for empress (by Luuk). * Fixed a case of slow range searching. * Configure fixes (`Docs' directory). * Added function `REVERSE()' (by Zeev Suraski). Changes in release 3.21.18 -------------------------- * Issue error message if client C functions are called in wrong order. * Added automatic reconnect to the `libmysql.c' library. If a write command fails, an automatic reconnect is done. * Small sort sets no longer use temporary files. * Upgraded `DBI' to 0.91. * Fixed a couple of problems with `LEFT OUTER JOIN'. * Added `CROSS JOIN' syntax. `CROSS' is now a reserved word. * Recoded `yacc'/`bison' stack allocation to be even safer and to allow *MySQL* to handle even bigger expressions. * Fixed a couple of problems with the update log. * `ORDER BY' was slow when used with key ranges. Changes in release 3.21.17 -------------------------- * Changed documentation string of `--with-unix-socket-path' to avoid confusion. * Added ODBC and ANSI SQL style `LEFT OUTER JOIN'. * The following are new reserved words: `LEFT', `NATURAL', `USING'. * The client library now uses the value of the environment variable `MYSQL_HOST' as the default host if it's defined. * `SELECT column, SUM(expr)' now returns `NULL' for `column' when there are matching rows. * Fixed problem with comparing binary strings and `BLOB's with ASCII characters over 127. * Fixed lock problem: when freeing a read lock on a table with multiple read locks, a thread waiting for a write lock would have been given the lock. This shouldn't affect data integrity, but could possibly make `mysqld' restart if one thread was reading data that another thread modified. * `LIMIT offset,count' didn't work in `INSERT ... SELECT'. * Optimized key block caching. This will be quicker than the old algorithm when using bigger key caches. Changes in release 3.21.16 -------------------------- * Added ODBC 2.0 & 3.0 functions `POWER()', `SPACE()', `COT()', `DEGREES()', `RADIANS()', `ROUND(2 arg)' and `TRUNCATE()'. * *WARNING: INCOMPATIBLE CHANGE!!* `LOCATE()' parameters were swapped according to ODBC standard. Fixed. * Added function `TIME_TO_SEC()'. * In some cases, default values were not used for `NOT NULL' fields. * Timestamp wasn't always updated properly in `UPDATE SET ...' statements. * Allow empty strings as default values for `BLOB' and `TEXT', to be compatible with `mysqldump'. Changes in release 3.21.15 -------------------------- * *WARNING: INCOMPATIBLE CHANGE!!* `mysqlperl' is now from Msql-Mysql-modules. This means that `connect()' now takes `host', `database', `user', `password' arguments! The old version took `host', `database', `password', `user'. * Allow `DATE '1997-01-01'', `TIME '12:10:10'' and `TIMESTAMP '1997-01-01 12:10:10'' formats required by ANSI SQL. *WARNING: INCOMPATIBLE CHANGE!!* This has the unfortunate side-effect that you no longer can have columns named `DATE', `TIME' or `TIMESTAMP'. :( Old columns can still be accessed through `tablename.columnname'!) * Changed Makefiles to hopefully work better with BSD systems. Also, `manual.dvi' is now included in the distribution to avoid having stupid `make' programs trying to rebuild it. * `readline' library upgraded to version 2.1. * A new sortorder german-1. That is a normal ISO-Latin1 with a german sort order. * Perl `DBI'/`DBD' is now included in the distribution. `DBI' is now the recommended way to connect to *MySQL* from Perl. * New portable benchmark suite with `DBD', with test results from `mSQL' 2.0.3, *MySQL*, PostgreSQL 6.2.1 and Solid server 2.2. * `crash-me' is now included with the benchmarks; This is a Perl program designed to find as many limits as possible in a SQL server. Tested with `mSQL', PostgreSQL, Solid and *MySQL*. * Fixed bug in range-optimizer that crashed *MySQL* on some queries. * Table and column name completion for `mysql' command line tool, by Zeev Suraski and Andi Gutmans. * Added new command `REPLACE' that works like `INSERT' but replaces conflicting records with the new record. `REPLACE INTO TABLE ... SELECT ...' works also. * Added new commands `CREATE DATABASE db_name' and `DROP DATABASE db_name'. * Added `RENAME' option to `ALTER TABLE': `ALTER TABLE name RENAME AS new_name'. * `make_binary_distribution' now includes `libgcc.a' in `libmysqlclient.a'. This should make linking work for people who don't have `gcc'. * Changed `net_write()' to `my_net_write()' because of a name conflict with Sybase. * New function `DAYOFWEEK()' compatible with ODBC. * Stack checking and `bison' memory overrun checking to make *MySQL* safer with weird queries. Changes in release 3.21.14b --------------------------- * Fixed a couple of small `configure' problems on some platforms. Changes in release 3.21.14a --------------------------- * Ported to SCO Openserver 5.0.4 with FSU-threads. * HP-UX 10.20 should work. * Added new function `DATE_FORMAT()'. * Added `NOT IN'. * Added automatic removal of 'ODBC function conversions': `{fn now() }' * Handle ODBC 2.50.3 option flags. * Fixed comparison of `DATE' and `TIME' values with `NULL'. * Changed language name from germany to german to be consistent with the other language names. * Fixed sorting problem on functions returning a `FLOAT'. Previously, the values were converted to `INT's before sorting. * Fixed slow sorting when sorting on key field when using `key_column=constant'. * Sorting on calculated `DOUBLE' values sorted on integer results instead. * `mysql' no longer needs a database argument. * Changed the place where `HAVING' should be. According to ANSI, it should be after `GROUP BY' but before `ORDER BY'. *MySQL* 3.20 incorrectly had it last. * Added Sybase command `USE DATABASE' to start using another database. * Added automatic adjusting of number of connections and table cache size if the maximum number of files that can be opened is less than needed. This should fix that `mysqld' doesn't crash even if you haven't done a `ulimit -n 256' before starting `mysqld'. * Added lots of limit checks to make it safer when running with too little memory or when doing weird queries. Changes in release 3.21.13 -------------------------- * Added retry of interrupted reads and clearing of `errno'. This makes Linux systems much safer! * Fixed locking bug when using many aliases on the same table in the same `SELECT'. * Fixed bug with `LIKE' on number key. * New error message so you can check whether the connection was lost while the command was running or whether the connection was down from the start. * Added `--table' option to `mysql' to print in table format. Moved time and row information after query result. Added automatic reconnect of lost connections. * Added `!=' as a synonym for `<>'. * Added function `VERSION()' to make easier logs. * New multi-user test `tests/fork_test.pl' to put some strain on the thread library. Changes in release 3.21.12 -------------------------- * Fixed `ftruncate()' call in MIT-pthreads. This made `isamchk' destroy the `.ISM' files on (Free)BSD 2.# systems. * Fixed broken `__P_' patch in MIT-pthreads. * Many memory overrun checks. All string functions now return `NULL' if the returned string should be longer than `max_allowed_packet' bytes. * Changed the name of the `INTERVAL' type to `ENUM', because `INTERVAL' is used in ANSI SQL. * In some cases, doing a `JOIN' + `GROUP' + `INTO OUTFILE', the result wasn't grouped. * `LIKE' with `'_'' as last character didn't work. Fixed. * Added extended ANSI SQL `TRIM()' function. * Added `CURTIME()'. * Added `ENCRYPT()' function by Zeev Suraski. * Fixed better `FOREIGN KEY' syntax skipping. New reserved words: `MATCH', `FULL', `PARTIAL'. * `mysqld' now allows IP number and hostname to the `--bind-address' option. * Added `SET OPTION CHARACTER SET cp1251_koi8' to enable conversions of data to/from cp1251_koi8. * Lots of changes for Win95 port. In theory, this version should now be easily portable to Win95. * Changed the `CREATE COLUMN' syntax of `NOT NULL' columns to be after the `DEFAULT' value, as specified in the ANSI SQL standard. This will make `mysqldump' with `NOT NULL' and default values incompatible with *MySQL* 3.20. * Added many function name aliases so the functions can be used with ODBC or ANSI SQL92 syntax. * Fixed syntax of `ALTER TABLE tbl_name ALTER COLUMN col_name SET DEFAULT NULL'. * Added `CHAR' and `BIT' as synonyms for `CHAR(1)'. * Fixed core dump when updating as a user who has only *select* privilege. * `INSERT ... SELECT ... GROUP BY' didn't work in some cases. An `Invalid use of group function' error occurred. * When using `LIMIT', `SELECT' now always uses keys instead of record scan. This will give better performance on `SELECT' and a `WHERE' that matches many rows. * Added Russian error messages. Changes in release 3.21.11 -------------------------- * Configure changes. * *MySQL* now works with the new thread library on BSD/OS 3.0. * Added new group functions `BIT_OR()' and `BIT_AND()'. * Added compatibility functions `CHECK' and `REFERENCES'. `CHECK' is now a reserved word. * Added `ALL' option to `GRANT' for better compatibility. (`GRANT' is still a dummy function.) * Added partly-translated dutch messages. * Fixed bug in `ORDER BY' and `GROUP BY' with `NULL' columns. * Added function `last_insert_id()' to retrieve last `AUTO_INCREMENT' value. This is intended for clients to ODBC that can't use the `mysql_insert_id()' API function, but can be used by any client. * Added `--flush-logs' option to `mysqladmin'. * Added command `STATUS' to `mysql'. * Fixed problem with `ORDER BY'/`GROUP BY' because of bug in `gcc'. * Fixed problem with `INSERT ... SELECT ... GROUP BY'. Changes in release 3.21.10 -------------------------- * New `mysqlaccess'. * `CREATE' now supports all ODBC types and the `mSQL' `TEXT' type. All ODBC 2.5 functions are also supported (added `REPEAT'). This provides better portability. * Added text types `TINYTEXT', `TEXT', `MEDIUMTEXT' and `LONGTEXT'. These are actually `BLOB'types, but all searching is done in case-insensitive fashion. * All old `BLOB' fields are now `TEXT' fields. This only changes that all searching on strings is done in case-sensitive fashion. You must do an `ALTER TABLE' and change the field type to `BLOB' if you want to have tests done in case-sensitive fashion. * Fixed some `configure' issues. * Made the locking code a bit safer. Fixed very unlikely deadlock situation. * Fixed a couple of bugs in the range optimizer. Now the new range benchmark `test-select' works. Changes in release 3.21.9 ------------------------- * Added `--enable-unix-socket=pathname' option to `configure'. * Fixed a couple of portability problems with include files. * Fixed bug in range calculation that could return empty set when searching on multiple key with only one entry (very rare). * Most things ported to FSU threads, which should allow *MySQL* to run on SCO. *Note SCO::. Changes in release 3.21.8 ------------------------- * Works now in Solaris 2.6. * Added handling of calculation of `SUM()' functions. For example, you can now use `SUM(column)/COUNT(column)'. * Added handling of trigometric functions: `PI()', `ACOS()', `ASIN()', `ATAN()', `COS()', `SIN()' and `TAN()'. * New languages: norwegian, norwegian-ny and portuguese. * Fixed parameter bug in `net_print()' in `procedure.cc'. * Fixed a couple of memory leaks. * Now allow also the old `SELECT ... INTO OUTFILE' syntax. * Fixed bug with `GROUP BY' and `SELECT' on key with many values. * `mysql_fetch_lengths()' sometimes returned incorrect lengths when you used `mysql_use_result()'. This affected at least some cases of `mysqldump --quick'. * Fixed bug in optimization of `WHERE const op field'. * Fixed problem when sorting on `NULL' fields. * Fixed a couple of 64-bit (Alpha) problems. * Added `--pid-file=#' option to `mysqld'. * Added date formatting to `FROM_UNIXTIME()', originally by Zeev Suraski. * Fixed bug in `BETWEEN' in range optimizer (Did only test = of the first argument). * Added machine-dependent files for MIT-pthreads i386-SCO. There is probably more to do to get this to work on SCO 3.5. Changes in release 3.21.7 ------------------------- * Changed `Makefile.am' to take advantage of Automake 1.2. * Added the beginnings of a benchmark suite. * Added more secure password handling. * Added new client function `mysql_errno()', to get the error number of the error message. This makes error checking in the client much easier. This makes the new server incompatible with the 3.20.# server when running without `--old-protocol'. The client code is backward compatible. More information can be found in the `README' file! * Fixed some problems when using very long, illegal names. Changes in release 3.21.6 ------------------------- * Fixed more portability issues (incorrect `sigwait' and `sigset' defines). * `configure' should now be able to detect the last argument to `accept()'. Changes in release 3.21.5 ------------------------- * Should now work with FreeBSD 3.0 if used with `FreeBSD-3.0-libc_r-1.0.diff', which can be found at `http://www.tcx.se/Download/Patches'. * Added new option `-O tmp_table_size=#' to `mysqld'. * New function `FROM_UNIXTIME(timestamp)' which returns a date string in 'YYYY-MM-DD HH:MM:DD' format. * New function `SEC_TO_TIME(seconds)' which returns a string in 'HH:MM:SS' format. * New function `SUBSTRING_INDEX()', originally by Zeev Suraski. Changes in release 3.21.4 ------------------------- * Should now configure and compile on OSF1 4.0 with the DEC compiler. * Configuration and compilation on BSD/OS 3.0 works, but due to some bugs in BSD/OS 3.0, `mysqld' doesn't work on it yet. * Configuration and compilation on FreeBSD 3.0 works, but I couldn't get `pthread_create' to work. Changes in release 3.21.3 ------------------------- * Added reverse check lookup of hostnames to get better security. * Fixed some possible buffer overflows if filenames that are too long are used. * `mysqld' doesn't accept hostnames that start with digits followed by a `'.'', because the hostname may look like an IP number. * Added `--skip-networking' option to `mysqld', to only allow socket connections. (This will not work with MIT-pthreads!) * Added check of too long table names for alias. * Added check if database name is okay. * Added check if too long table names. * Removed incorrect `free()' that killed the server on `CREATE DATABASE' or `DROP DATABASE'. * Changed some `mysqld' `-O' options to better names. * Added `-O join_cache_size=#' option to `mysqld'. * Added `-O max_join_size=#' option to `mysqld', to be able to set a limit how big queries (in this case big = slow) one should be able to handle without specifying `SET OPTION SQL_BIG_SELECTS=1'. A # = is about 10 examined records. The default is "unlimited". * When comparing a `TIME', `DATE', `DATETIME' or `TIMESTAMP' column to a constant, the constant is converted to a time value before performing the comparison. This will make it easier to get ODBC (particularly Access97) to work with the above types. It should also make dates easier to use and the comparisons should be quicker than before. * Applied patch from Jochen Wiedmann that allows `query()' in `mysqlperl' to take a query with `\0' in it. * Storing a timestamp with a 2-digit year (`YYMMDD') didn't work. * Fix that timestamp wasn't automatically updated if set in an `UPDATE' clause. * Now the automatic timestamp field is the FIRST timestamp field. * `SELECT * INTO OUTFILE', which didn't correctly if the outfile already existed. * `mysql' now shows the thread ID when starting or doing a reconnect. * Changed the default sort buffer size from 2M to 1M. Changes in release 3.21.2 ------------------------- * The range optimizer is coded, but only 85% tested. It can be enabled with `--new', but it crashes core a lot yet... * More portable. Should compile on AIX and alpha-digital. At least the `isam' library should be relatively 64-bit clean. * New `isamchk' which can detect and fix more problems. * New options for `isamlog'. * Using new version of Automake. * Many small portability changes (from the AIX and alpha-digital port) Better checking of pthread(s) library. * czech error messages by . * Decreased size of some buffers to get fewer problems on systems with little memory. Also added more checks to handle "out of memory" problems. * `mysqladmin': you can now do `mysqladmin kill 5,6,7,8' to kill multiple threads. * When the maximum connection limit is reached, one extra connection by a user with the *PROCESS_ACL* privilege is granted. * Added `-O backlog=#' option to `mysqld'. * Increased maximum packet size from 512K to 1024K for client. * Almost all of the function code is now tested in the internal test suite. * `ALTER TABLE' now returns warnings from field conversions. * Port changed to 3306 (got it reserved from ISI). * Added a fix for Visual FoxBase so that any schema name from a table specification is automatically removed. * New function `ASCII()'. * Removed function `BETWEEN(a,b,c)'. Use the standard ANSI synax instead: `expr BETWEEN expr AND expr'. * *MySQL* no longer has to use an extra temporary table when sorting on functions or `SUM()' functions. * Fixed bug that you couldn't use `tbl_name.field_name' in `UPDATE'. * Fixed `SELECT DISTINCT' when using 'hidden group'. For example: mysql> SELECT DISTINCT MOD(some_field,10) FROM test GROUP BY some_field; Note: `some_field' is normally in the `SELECT' part. ANSI SQL should require it. Changes in release 3.21.0 ------------------------- * New keywords used: `INTERVAL', `EXPLAIN', `READ', `WRITE', `BINARY'. * Added ODBC function `CHAR(num,...)'. * New operator `IN'. This uses a binary search to find a match. * New command `LOCK TABLES tbl_name [AS alias] {READ|WRITE} ...' * Added `--log-update' option to `mysqld', to get a log suitable for incremental updates. * New command `EXPLAIN SELECT ...' to get information about how the optimizer will do the join. * For easier client code, the client should no longer use `FIELD_TYPE_TINY_BLOB', `FIELD_TYPE_MEDIUM_BLOB', `FIELD_TYPE_LONG_BLOB' or `FIELD_TYPE_VAR_STRING' (as previously returned by `mysql_list_fields'). You should instead only use `FIELD_TYPE_BLOB' or `FIELD_TYPE_STRING'. If you want exact types, you should use the command `SHOW FIELDS'. * Added varbinary syntax: `0x######' which can be used as a string (default) or a number. * `FIELD_TYPE_CHAR' is renamed to `FIELD_TYPE_TINY'. * Changed all fields to C++ classes. * Removed FORM struct. * Fields with `DEFAULT' values no longer need to be `NOT NULL'. * New field types: `ENUM' A string which can take only a couple of defined values. The value is stored as a 1-3 byte number that is mapped automatically to a string. This is sorted according to string positions! `SET' A string which may have one or many string values separated with ','. The string is stored as a 1-, 2-, 3-, 4- or 8-byte number where each bit stands for a specific set member. This is sorted according to the unsigned value of the stored packed number. * Now all function calculation is done with `double' or `long long'. This will provide the full 64-bit range with bit functions and fix some conversions that previously could result in precision losses. One should avoid using `unsigned long long' columns with full 64-bit range (numbers bigger than 9223372036854775807) because calculations are done with `signed long long'. * `ORDER BY' will now put `NULL' field values first. `GROUP BY' will also work with `NULL' values. * Full `WHERE' with expressions. * New range optimizer that can resolve ranges when some keypart prefix is constant. Example: mysql> SELECT * FROM tbl_name WHERE key_part_1="customer" AND key_part_2>=10 AND key_part_2<=10; Changes in release 3.20.x ========================= Changes from 3.20.18 to 3.20.32b are not documented here since the 3.21 release branched here. And the relevant changes are also documented as changes to the 3.21 version. Changes in release 3.20.18 -------------------------- * Added `-p#' (remove `#' directories from path) to `isamlog'. All files are written with a relative path from the database directory Now `mysqld' shouldn't crash on shutdown when using the `--log-isam' option. * New `mysqlperl' version. It is now compatible with `msqlperl-0.63'. * New `DBD' module available at `http://www.tcx.se/Contrib' site. * Added group function `STD()' (standard deviation). * The `mysqld' server is now compiled by default without debugging information. This will make the daemon smaller and faster. * Now one usually only has to specify the `--basedir' option to `mysqld'. All other paths are relative in a normal installation. * `BLOB' columns sometimes contained garbage when used with a `SELECT' on more than one table and `ORDER BY'. * Fixed that calculations that are not in `GROUP BY' work as expected (ANSI SQL extension). Example: mysql> SELECT id,id+1 FROM table GROUP BY id; * The test of using `MYSQL_PWD' was reversed. Now `MYSQL_PWD' is enabled as default in the default release. * Fixed conversion bug which caused `mysqld' to core dump with Arithmetic error on Sparc-386. * Added `--unbuffered' option to `mysql', for new `mysqlaccess'. * When using overlapping (unnecessary) keys and join over many tables, the optimizer could get confused and return 0 records. Changes in release 3.20.17 -------------------------- * You can now use `BLOB' columns and the functions `IS NULL' and `IS NOT NULL' in the `WHERE' clause. * All communication packages and row buffers are now allocated dynamically on demand. The default value of `max_allowed_packet' is now 65K for the server and 512K for the client. This is mainly used to catch incorrect packets that could trash all memory. The server limit may be changed when it is started. * Changed stack usage to use less memory. * Changed `safe_mysqld' to check for running daemon. * The `ELT()' function is renamed to `FIELD()'. The new `ELT()' function returns a value based on an index: `FIELD()' is the inverse of `ELT()' Example: `ELT(2,"A","B","C")' returns `"B"'. `FIELD("B","A","B","C")' returns `2'. * `COUNT(field)', where `field' could have a `NULL' value, now works. * A couple of bugs fixed in `SELECT ... GROUP BY'. * Fixed memory overrun bug in `WHERE' with many unoptimizable brace levels. * Fixed some small bugs in the grant code. * If hostname isn't found by `get_hostname', only the IP is checked. Previously, you got `Access denied'. * Inserts of timestamps with values didn't always work. * `INSERT INTO ... SELECT ... WHERE' could give the error `Duplicated field'. * Added some tests to `safe_mysqld' to make it "safer". * `LIKE' was case sensitive in some places and case insensitive in others. Now `LIKE' is always case insensitive. * `mysql.cc': Allow `'#'' anywhere on the line. * New command `SET OPTION SQL_SELECT_LIMIT=#'. See the FAQ for more details. * New version of the `mysqlaccess' script. * Change `FROM_DAYS()' and `WEEKDAY()' to also take a full `TIMESTAMP' or `DATETIME' as argument. Before they only took a number of type `YYYYMMDD' or `YYMMDD'. * Added new function `UNIX_TIMESTAMP(timestamp_column)'. Changes in release 3.20.16 -------------------------- * More changes in MIT-pthreads to get them safer. Fixed also some link bugs at least in SunOS. * Changed `mysqld' to work around a bug in MIT-pthreads. This makes multiple small `SELECT' operations 20 times faster. Now `lock_test.pl' should work. * Added `mysql_FetchHash(handle)' to `mysqlperl'. * The `mysqlbug' script is now distributed built to allow for reporting bugs that appear during the build with it. * Changed `libmysql.c' to prefer `getpwuid()' instead of `cuserid()'. * Fixed bug in `SELECT' optimizer when using many tables with the same column used as key to different tables. * Added new latin2 and Russian KOI8 character tables. * Added support for a dummy `GRANT' command to satisfy Powerbuilder. Changes in release 3.20.15 -------------------------- * Fixed fatal bug `packets out of order' when using MIT-pthreads. * Removed possible loop when a thread waits for command from client and `fcntl()' fails. Thanks to Mike Bretz for finding this bug. * Changed alarm loop in `mysqld.cc' because shutdown didn't always succeed in Linux. * Removed use of `termbits' from `mysql.cc'. This conflicted with `glibc' 2.0. * Fixed some syntax errors for at least BSD and Linux. * Fixed bug when doing a `SELECT' as superuser without a database. * Fixed bug when doing `SELECT' with group calculation to outfile. Changes in release 3.20.14 -------------------------- * If one gives `-p' or `--password' option to `mysql' without an argument, the user is solicited for the password from the tty. * Added default password from `MYSQL_PWD' (by Elmar Haneke). * Added command `kill' to `mysqladmin' to kill a specific *MySQL* thread. * Sometimes when doing a reconnect on a down connection this succeeded first on second try. * Fixed adding an `AUTO_INCREMENT' key with `ALTER_TABLE'. * `AVG()' gave too small value on some `SELECT's with `GROUP BY' and `ORDER BY'. * Added new `DATETIME' type (by Giovanni Maruzzelli ). * Fixed that define `DONT_USE_DEFAULT_FIELDS' works. * Changed to use a thread to handle alarms instead of signals on Solaris to avoid race conditions. * Fixed default length of signed numbers. (George Harvey .) * Allow anything for `CREATE INDEX'. * Add prezeros when packing numbers to `DATE', `TIME' and `TIMESTAMP'. * Fixed a bug in `OR' of multiple tables (gave empty set). * Added many patches to MIT-pthreads. This fixes at least one lookup bug. Changes in release 3.20.13 -------------------------- * Added ANSI SQL94 `DATE' and `TIME' types. * Fixed bug in `SELECT' with `AND'-`OR' levels. * Added support for Slovenian characters. The `Contrib' directory contains source and instructions for adding other character sets. * Fixed bug with `LIMIT' and `ORDER BY'. * Allow `ORDER BY' and `GROUP BY' on items that aren't in the `SELECT' list. (Thanks to Wim Bonis , for pointing this out.) * Allow setting of timestamp values in `INSERT'. * Fixed bug with `SELECT ... WHERE ... = NULL'. * Added changes for `glibc' 2.0. To get `glibc' to work, you should add the `gibc-2.0-sigwait-patch' before compiling `glibc'. * Fixed bug in `ALTER TABLE' when changing a `NOT NULL' field to allow `NULL' values. * Added some ANSI92 synonyms as field types to `CREATE TABLE'. `CREATE TABLE' now allows `FLOAT(4)' and `FLOAT(8)' to mean `FLOAT' and `DOUBLE'. * New utility program `mysqlaccess' by . This program shows the access rights for a specific user and the grant rows that determine this grant. * Added `WHERE const op field' (by ). Changes in release 3.20.11 -------------------------- * When using `SELECT ... INTO OUTFILE', all temporary tables are ISAM instead of HEAP to allow big dumps. * Changed date functions to be string functions. This fixed some "funny" side effects when sorting on dates. * Extended `ALTER TABLE' according to SQL92. * Some minor compability changes. * Added `--port' and `--socket' options to all utility programs and `mysqld'. * Fixed MIT-pthreads `readdir_r()'. Now `mysqladmin create database' and `mysqladmin drop database' should work. * Changed MIT-pthreads to use our `tempnam()'. This should fix the "sort aborted" bug. * Added sync of records count in `sql_update'. This fixed slow updates on first connection. (Thanks to Vaclav Bittner for the test.) Changes in release 3.20.10 -------------------------- * New insert type: `INSERT INTO ... SELECT ...' * `MEDIUMBLOB' fixed. * Fixed bug in `ALTER TABLE' and `BLOB's. * `SELECT ... INTO OUTFILE' now creates the file in the current database directory. * `DROP TABLE' now can take a list of tables. * Oracle synonym `DESCRIBE' (`DESC'). * Changes to `make_binary_distribution'. * Added some comments to installation instructions about `configure''s C++ link test. * Added `--without-perl' option to `configure'. * Lots of small portability changes. Changes in release 3.20.9 ------------------------- * `ALTER TABLE' didn't copy null bit. As a result, fields that were allowed to have `NULL' values were always `NULL'. * `CREATE' didn't take numbers as `DEFAULT'. * Some compatibility changes for SunOS. * Removed `config.cache' from old distribution. Changes in release 3.20.8 ------------------------- * Fixed bug with `ALTER TABLE' and multi-part keys. Changes in release 3.20.7 ------------------------- * New commands: `ALTER TABLE', `SELECT ... INTO OUTFILE' and `LOAD DATA INFILE'. * New function: `NOW()'. * Added new field *file_priv* to `mysql/user' table. * New script `add_file_priv' which adds the new field *file_priv* to the `user' table. This script must be executed if you want to use the new `SELECT ... INTO' and `LOAD DATA INFILE ...' commands with a version of *MySQL* earlier than 3.20.7. * Fixed bug in locking code, which made `lock_test.pl' test fail. * New files `NEW' and `BUGS'. * Changed `select_test.c' and `insert_test.c' to include `config.h'. * Added command `status' to `mysqladmin' for short logging. * Increased maximum number of keys to 16 and maximum number of key parts to 15. * Use of sub keys. A key may now be a prefix of a string field. * Added `-k' option to `mysqlshow', to get key information for a table. * Added long options to `mysqldump'. Changes in release 3.20.6 ------------------------- * Portable to more systems because of MIT-pthreads, which will be used automatically if `configure' cannot find a `-lpthreads' library. * Added GNU-style long options to almost all programs. Test with `program --help'. * Some shared library support for Linux. * The FAQ is now in `.texi' format and is available in `.html', `.txt' and `.ps' formats. * Added new SQL function `RAND([init])'. * Changed `sql_lex' to handle `\0' unquoted, but the client can't send the query through the C API, because it takes a str pointer. You must use `mysql_real_query()' to send the query. * Added API function `mysql_get_client_info()'. * `mysqld' now uses the `N_MAX_KEY_LENGTH' from `nisam.h' as the maximum allowed key length. * The following now works: mysql> SELECT filter_nr,filter_nr FROM filter ORDER BY filter_nr; Previously, this resulted in the error: `Column: 'filter_nr' in order clause is ambiguous'. * `mysql' now outputs `'\0'', `'\t'', `'\n'' and `'\\'' when encountering ASCII 0, tab, newline or `'\'' while writing tab-separated output. This is to allow printing of binary data in a portable format. To get the old behavior, use `-r' (or `--raw'). * Added german error messages (60 of 80 error messages translated). * Added new API function `mysql_fetch_lengths(MYSQL_RES *)', which returns an array of of column lengths (of type `uint'). * Fixed bug with `IS NULL' in `WHERE' clause. * Changed the optimizer a little to get better results when searching on a key part. * Added `SELECT' option `STRAIGHT_JOIN' to tell the optimizer that it should join tables in the given order. * Added support for comments starting with `'--'' in `mysql.cc' (Postgres syntax). * You can have `SELECT' expressions and table columns in a `SELECT' which are not used in the group part. This makes it efficient to implement lookups. The column that is used should be a constant for each group because the value is calculated only once for the first row that is found for a group. mysql> SELECT id,lookup.text,sum(*) FROM test,lookup WHERE test.id=lookup.id GROUP BY id; * Fixed bug in `SUM(function)' (could cause a core dump). * Changed `AUTO_INCREMENT' placement in the SQL query: INSERT into table (auto_field) values (0); inserted 0, but it should insert an `AUTO_INCREMENT' value. * `mysqlshow.c': Added number of records in table. Had to change the client code a little to fix this. * `mysql' now allows doubled `''' or `""' within strings for embedded `'' or `"'. * New math functions: `EXP()', `LOG()', `SQRT()', `ROUND()', `CEILING()'. Changes in release 3.20.3 ------------------------- * The `configure' source now compiles a thread-free client library `-lmysqlclient'. This is the only library that needs to be linked with client applications. When using the binary releases, you must link with `-lmysql -lmysys -ldbug -lstrings' as before. * New `readline' library from `bash-2.0'. * LOTS of small changes to `configure' and makefiles (and related source). * It should now be possible to compile in another directory using `VPATH'. Tested with GNU Make 3.75. * `safe_mysqld' and `mysql.server' changed to be more compatible between the source and the binary releases. * `LIMIT' now takes one or two numeric arguments. If one argument is given, it indicates the maximum number of rows in a result. If two arguments are given, the first argument indicates the offset of the first row to return, the second is the maximum number of rows. With this it's easy to do a poor man's next page/previous page WWW application. * Changed name of SQL function `FIELDS()' to `ELT()'. Changed SQL function `INTERVALL()' to `INTERVAL()'. * Made `SHOW COLUMNS' a synonym for `SHOW FIELDS'. Added compatibility syntax `FRIEND KEY' to `CREATE TABLE'. In *MySQL*, this creates a non-unique key on the given columns. * Added `CREATE INDEX' and `DROP INDEX' as compatibility functions. In *MySQL*, `CREATE INDEX' only checks if the index exists and issues an error if it doesn't exist. `DROP INDEX' always succeeds. * `mysqladmin.c': added client version to version information. * Fixed core dump bug in `sql_acl' (core on new connection). * Removed `host', `user' and `db' tables from database `test' in the distribution. * `FIELD_TYPE_CHAR' can now be signed (-128 - 127) or unsigned (0 - 255) Previously, it was always unsigned. * Bug fixes in `CONCAT()' and `WEEKDAY()'. * Changed a lot of source to get `mysqld' to be compiled with SunPro compiler. * SQL functions must now have a `'('' immediately after the function name (no intervening space). For example, `'user('' is regarded as beginning a function call, and `'user ('' is regarded as an identifier `user' followed by a `'('', not as a function call. Changes in release 3.20.0 ------------------------- * The source distribution is done with `configure' and Automake. It will make porting much easier. The `readline' library is included in the distribution. * Separate client compilation: the client code should be very easy to compile on systems which don't have threads. * The old Perl interface code is automatically compiled and installed. Automatic compiling of `DBD' will follow when the new `DBD' code is ported. * Dynamic language support: `mysqld' can now be started with Swedish or English (default) error messages. * New functions: `INSERT()', `RTRIM()', `LTRIM()' and `FORMAT()'. * `mysqldump' now works correctly for all field types (even `AUTO_INCREMENT'). The format for `SHOW FIELDS FROM tbl_name' is changed so the `Type' column contains information suitable for `CREATE TABLE'. In previous releases, some `CREATE TABLE' information had to be patched when recreating tables. * Some parser bugs from 3.19.5 (`BLOB' and `TIMESTAMP') are corrected. `TIMESTAMP' now returns different date information depending on its create length. * Changed parser to allow a database, table or field name to start with a number or `'_''. * All old C code from Unireg changed to C++ and cleaned up. This makes the daemon a little smaller and easier to understand. * A lot of small bug fixes done. * New INSTALL files (not final version) and some info regarding porting. Changes in release 3.19.x ========================= Changes in release 3.19.5 ------------------------- * Some new functions, some more optimization on joins. * Should now compile clean on Linux (2.0.x). * Added functions `DATABASE()', `USER()', `POW()', `LOG10()' (needed for ODBC). * In a `WHERE' with an `ORDER BY' on fields from only one table, the table is now preferred as first table in a multi-join. * `HAVING' and `IS NULL' or `IS NOT NULL' now works. * A group on one column and a sort on a group function (`SUM()', `AVG()'...) didn't work together. Fixed. * `mysqldump': Didn't send password to server. Changes in release 3.19.4 ------------------------- * Fixed horrible locking bug when inserting in one thread and reading in another thread. * Fixed one-off decimal bug. 1.00 was output as 1.0. * Added attribute `'Locked'' to process list as info if a query is locked by another query. * Fixed full magic timestamp. Timestamp length may now be 14, 12, 10, 8, 6, 4 or 2 bytes. * Sort on some numeric functions could sort incorrectly on last number. * `IF(arg,syntax_error,syntax_error)' crashed. * Added functions `CEILING()', `ROUND()', `EXP()', `LOG()' and `SQRT()'. * Enhanced `BETWEEN' to handle strings. Changes in release 3.19.3 ------------------------- * Fixed `SELECT' with grouping on `BLOB' columns not to return incorrect `BLOB' info. Grouping, sorting and distinct on `BLOB' columns will not yet work as expected (probably it will group/sort by the first 7 characters in the `BLOB'). Grouping on formulas with a fixed string size (use `MID()' on a `BLOB') should work. * When doing a full join (no direct keys) on multiple tables with `BLOB' fields, the `BLOB' was garbage on output. * Fixed `DISTINCT' with calculated columns. Known errors and design deficiencies in *MySQL* *********************************************** * You cannot build in another directory when using MIT-pthreads. Since this requires changes to MIT-pthreads, we are not likely to fix this. * `BLOB's can't "reliably" be used in `GROUP BY' or `ORDER BY' or `DISTINCT'. Only the first `max_sort_length' bytes (default 1024) are used when comparing `BLOB'bs in these cases. This can be changed with the `-O max_sort_length' option to `mysqld'. A workaround for most cases is to use a substring: `SELECT DISTINCT LEFT(blob,2048) FROM tbl_name'. * Calculation is done with `BIGINT' or `DOUBLE' (both are normally 64 bits long). It depends on the function which precision one gets. The general rule is that bit functions are done with `BIGINT' precision, `IF', and `ELT()' with `BIGINT' or `DOUBLE' precision and the rest with `DOUBLE' precision. One should try to avoid using bigger unsigned long long values than 63 bits (9223372036854775807) for anything else than bit fields! * All numeric types are treated as fixed-point fields. That means you must specify how many decimals a floating-point field shall have. All results will be returned with the correct number of decimals. * All string columns, except `BLOB' and `TEXT' columns, automatically have all trailing spaces removed when retrieved. For `CHAR' types this is okay, and may be regarded as a feature according to ANSI SQL92. The bug is that `VARCHAR' columns are treated the same way. * You can only have up to 255 `ENUM' and `SET' columns in one table. * An `UPDATE' that updates a key with a `WHERE' on the same key may fail because the key is used to search for records and will be found multiple times: UPDATE SET KEY=KEY+1 WHERE KEY > 100; This will be fixed in newer *MySQL* versions by not using keys that contain fields that are going to be updated. Until this fixed you can use the current workaround: mysql> UPDATE SET KEY=KEY+1 WHERE KEY+0 > 100; This will work because *MySQL* will not use index on expressions in the `WHERE' clause. * `safe_mysqld' re-directs all messages from `mysqld' to the `mysqld' log. One problem with this is that if you execute `mysqladmin refresh' to close and reopen the log, `stdout' and `stderr' are still redirected to the old log. If you use `--log' extensively, you should edit `safe_mysqld' to log to `'hostname'.err' instead of `'hostname'.log' so you can easily reclaim the space for the old log by deleting the old one and executing `mysqladmin refresh'. For platform-specific bugs, see the sections about compiling and porting. List of things we want to add to *MySQL* in the future (The TODO) ***************************************************************** Everything in this list is in the order it will be done. If you want to affect the priority order, please register a license or support us and tell us what you want to have done more quickly. *Note Licensing and Support::. Things that must done in the real near future ============================================= * Binary compatible ISAM tables. * Subqueries. `select id from t where grp in (select grp from g where u > 100)' * Delayed inserts for log tables. * If one does an `ALTER TABLE' on a table that is symlinked to another disk, create temporary tables on this disk. * FreeBSD and MIT-pthreads; Do sleeping threads take CPU? * Allow join on key parts (optimizing issue). * Automatically convert temporary HEAP tables to NISAM if they get too big. At the moment you get `error 135' or `Table xxx is full' if you execute a query which has to use a big temporary table. * Binary portable data tables (a new version of ISAM). * Add `DISTINCT' qualifier to `COUNT()', `SUM()'... * Change conv_blob to handle `BLOB' as a `TEXT' field. * Entry for `DECRYPT()'. * Remember `FOREIGN' key definitions in the `.frm' file. * Server side cursors. * Don't add automatic `DEFAULT' values to columns. Give an error when using an `INSERT' that doesn't contain a column that doesn't have a `DEFAULT'. * Caching of queries and results. This should be done as a separated module that examines each query and if this is query is in the cache the cached result should be returned. When one updates a table one should remove as few queries as possible from the cache. This should give a big speed bost on machines with much RAM where queries are often repeated (like WWW applications). One idea would be to only cache queries of type: `SELECT CACHED ....' * Fix `libmysql.c' to allow two `mysql_query()' commands in a row without reading results or give a nice error message when one does this. * Optimize `BIT' type to take 1 bit (now `BIT' takes 1 char). * Check why MIT-pthreads `ctime()' doesn't work on some FreeBSD systems. * Check if locked threads take any CPU. * Add `ORDER BY' to update. This would be handy with functions like: `generate_id(start,step)'. * Add an `IMAGE' option to `LOAD DATA INFILE' to not update `TIMESTAMP' and `AUTO_INCREMENT' fields. * Make `LOAD DATA INFILE' understand a syntax like: LOAD DATA INFILE 'file_name.txt' INTO TABLE tbl_name TEXT_FIELDS (text_field1, text_field2, text_field3) SET table_field1=concatenate(text_field1, text_field2), table_field3=23 IGNORE text_field3 * Allow strings with `MIN()', `MAX()' (not group functions). These should be synonyms for `LEAST()', `GREATEST()'. * Demo procedure: analyze * Automatic output from `mysql' to netscape. * `LOCK DATABASES'. (with various options) * `NATURAL JOIN'. * Change sort to allocate memory in "hunks" to get better memory utilization. * `DECIMAL' and `NUMERIC' types can't read exponential numbers; `Field_decimal::store(const char *from,uint len)' must be recoded to fix this. * Add ANSI SQL `EXTRACT' function. * Fix `mysql.cc' to do fewer `malloc()' calls when hashing field names. * Add functions: EXPORT_SET(set_column,'Y','N',[separator],[number_of_set_values]) where `separator' is `','' by default and `number_of_set_values' is taken from the `set_column' (or is 64 if `set_column' is an expression). For example: EXPORT_SET(9,'Y','N',',',5) -> Y,N,N,Y,N * Add use of `t1 JOIN t2 ON ...' and `t1 JOIN t2 USING ...' Currently, you can only use this syntax with `LEFT JOIN'. * Add full support for `unsigned long long' type. * A `LOCK DATABASE' function (for backups). * Function `CASE'. * Much more variables for `show status'. Counts for: `INSERT'/`DELETE'/`UPDATE' statements. Records reads and updated. Selects on 1 table and selects with joins. Mean number of tables in select. Key buffer read/write hits (logical and real). `ORDER BY', `GROUP BY', temporary tables created. * If you abort `mysql' in the middle of a query, you should open another connection and kill the old running query. Alternatively, an attempt should be made to detect this in the server. * Add a handler interface for table information so you can use it as a system table. This would be a bit slow if you requested information about all tables, but very flexible. `SHOW INFO FROM tbl_name' for basic table information should be implemented. * Allow `mysqld' to support many character sets at the same time. * Add support for UNICODE. * Add optimization to make `LEFT JOIN .. WHERE not_null_field IS NULL' much faster. (This is often used to find rows that doesn't match) * Oracle like CONNECT BY PRIOR ... to search hierarchy structures. Things that have to be done sometime ==================================== * Implement a table optimizer by an analyze procedure call that returns a table like show fields with min and max value and the best *MySQL* type for that expression. * Implement function: `get_changed_tables(timeout,table1,table2,...)' * Implement function: `LAST_UPDATED(tbl_name)' * Atomic updates; This includes a language that one can even use for a set of stored procedures. * `update items,month set items.price=month.price where items.id=month.id;' * Change reading through tables to use memmap when possible. Now only compressed tables use memmap. * Make a SQL standard `GRANT' command with *MySQL* extensions. * Add a new privilege *'Show_priv'* for `SHOW' commands. * Make the automatic timestamp code nicer. Add timestamps to the update log with `SET TIMESTAMP=#;' * Optimize the autoincrement code. * Use read/write mutex in some places to get more speed. * Full foreign key support. One probably wants to implement a procedural language first. * Simple views (first on one table, later on any expression). * Automatically close some tables if a table, temporary table or temporary files gets error 23 (not enough open files). * When one finds a field=#, change all occurrences of field to #. Now this is only done for some simple cases. * Change all const expressions with calculated expressions if possible. * Optimize key = expression. At the moment only key = field or key = constant are optimized. * Join some of the copy functions for nicer code. * Change `sql_yacc.yy' to an inline parser to reduce its size and get better error messages (5 days). * Change the parser to use only one rule per different number of arguments in function. * Use of full calculation names in the order part. (For ACCESS97) * `UNION', `MINUS', `INTERSECT' and `FULL OUTER JOIN'. (Currently only `LEFT OUTER JOIN' is supported) * Allow `UNIQUE' on fields that can be `NULL'. * `SQL_OPTION MAX_SELECT_TIME=#' to put a time limit on a query. * Make the update log to a database. * Negative `LIMIT' to retrieve data from the end. * Alarm around client connect/read/write functions. * Make a `mysqld' version which isn't multithreaded (3-5 days). * Please note the changes to `safe_mysqld': according to FSSTND (which Debian tries to follow) PID files should go into `/var/run/.pid' and log files into `/var/log'. It would be nice if you could put the "DATADIR" in the first declaration of "pidfile" and "log", so the placement of these files can be changed with a single statement. * Better dynamic record layout to avoid fragmentation. * `UPDATE SET blob=read_blob_from_file('my_gif') where id=1;' * Allow sorting on `RAND()': SELECT email,RAND() AS ran FROM info ORDER BY ran; * Allow a client to request logging. * Add use of `zlib()' for `gzip'-ed files to `LOAD DATA INFILE'. * Fix sorting and grouping of `BLOB' columns (partly solved now). * Stored procedures. This is currently not regarded to be very important as stored procedures are not very standardized yet. Another problem is that true stored procedures make it much harder for the optimizer and in many cases the result is slower than before We will, on the other hand, add a simple (atomic) update language that can be used to write loops and such in the *MySQL* server. * Change to use semaphores when counting threads. One should first implement a semaphore library to MIT-pthreads. * Don't assign a new `AUTO_INCREMENT' value when one sets a column to 0. Use `NULL' instead. Time is given according to amount of work, not real time. TcX's main business is the use of *MySQL* not the development of it. But since TcX is a very flexible company, we have put a lot of resources into the development of *MySQL*. Some things we don't have any plans to do ========================================= * Transactions with rollback (we mainly do `SELECT's, and because we don't do transactions, we can be much quicker on everything else). We will support some kind of atomic operations on multiple tables, though. Currently atomic operations can be done with `LOCK TABLES'/`UNLOCK TABLES' but we will make this more automatic in the future. Comments on porting to other systems ************************************ A working Posix thread library is needed for the server. On Solaris 2.5 we use SUN PThreads (the native thread support in 2.4 and earlier versions are not good enough) and on Linux we use LinuxThreads by Xavier Leroy, . The hard part of porting to a new Unix variant without good native thread support is probably to port MIT-pthreads. See `mit-pthreads/README' and Programming POSIX Threads (http://www.humanfactor.com/pthreads/). The *MySQL* distribution includes a patched version of Provenzano's Pthreads from MIT (see MIT Pthreads web page (http://www.mit.edu:8001/people/proven/pthreads.html)). This can be used for some operating systems that do not have POSIX threads. It is also possible to use another user level thread package named FSU Pthreads (see FSU pthread home page (http://www.informatik.hu-berlin.de/~mueller/pthreads.html)). This implementation is being used for the SCO port. See the `thr_lock.c' and `thr_alarm.c' programs in the `mysys' directory for some tests/examples of these problems. Both the server and the client need a working C++ compiler (we use `gcc' and have tried SparcWorks). Another compiler that is known to work is the IRIX `cc'. To compile only the client use `./configure --without-server'. There is currently no support for only compiling the server. Nor is it likly to be added unless someone has a good reason for it. If you want/need to change any `Makefile' or the configure script you must get Automake and Autoconf. We have used the `automake-1.2' and `autoconf-2.12' distributions. All steps needed to remake everything from the most basic files. /bin/rm */.deps/*.P /bin/rm -f config.cache aclocal autoheader aclocal automake autoconf ./configure --with-debug --prefix='your installation directory' # The makefiles generated above need GNU make 3.75 or newer. # (called gmake below) gmake clean all install init-db If you run into problems with a new port, you may have to do some debugging of *MySQL*! *Note Debugging::. *NOTE*: Before you start debugging `mysqld', first get the test programs `mysys/thr_alarm' and `mysys/thr_lock' to work. This will ensure that your thread installation has even a remote chance to work! Debugging *MySQL* ================= If you have some very specific problem, you can always try to debug *MySQL*. To do this you must configure *MySQL* with the option `--with-debug'. You can check whether or not *MySQL* was compiled with debugging by doing: `mysqld --help'. If the `--debug' flag is listed with the options then you have debugging enabled. `mysqladmin ver' also lists the `mysqld' version as `mysql ... -debug' in this case. If you are using gcc or egcs, the recommended configure line is: CC=gcc CFLAGS="-O6" CXX=gcc CXXFLAGS="-O6 -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-debug This will avoid problems with the libstdc++ library and with C++ exceptions. If you can cause the `mysqld' server to crash quickly, you can try to create a trace file of this: Start the `mysqld' server with a trace log in `/tmp/mysql.trace'. The log file will get very *BIG*. `mysqld --debug --log' or you can start it with `mysqld --debug=d,info,error,query,general,where:O,/tmp/mysql.trace' which only prints information with the most interesting tags. When you configure *MySQL* for debugging you automatically enable a lot of extra safety check functions that monitor the health of `mysqld'. If they find something "unexpected," an entry will be written to `stderr', which `safe_mysqld' directs to the error log! This also means that if you are having some unexpected problems with *MySQL* and are using a source distribution, the first thing you should do is to configure *MySQL* for debugging! (The second thing, of course, is to send mail to and ask for help. Please use the `mysqlbug' script for all bug reports or questions regarding the *MySQL* version you are using! On most system you can also start `mysqld' from `gdb' to get more information if `mysqld' crashes. shell> gdb /usr/local/libexec/mysqld gdb> run ... back # Do this when mysqld crashes info locals up info locals up ... (until you get some information about local variables) quit On Linux you must use `run --one-thread' if you want to be able to debug `mysqld' threads. In this case you can only have one thread active at a time. Include the above output in a mail generated with `mysqlbug' and mail this to `mysql@tcx.se'. If `mysqld' hangs you can try to use some system tools like `strace' or `/usr/proc/bin/pstack' to examine where `mysqld' has hanged. If `mysqld' starts to eat up CPU or memory or if it 'hangs', you can use `mysqladmin processlist status' to find out if someone is executing some query that takes a long time. It may be a good idea to run `mysqladmin -i10 processlist status' in some window if you are experiencing performance problems. If `mysqld' dies or hangs, you should start `mysqld' with `--log'. When `mysqld' dies again, you can check in the log file for the query that killed `mysqld'. Note that before starting `mysqld' with `--log' you should check all your tables with `isamchk'. *Note Maintenance::. If you are using a log file, `mysqld --log', you should check the 'hostname' log files, that you can find in the database directory, for any queries that could cause a problem. Try the command `EXPLAIN' on all `SELECT' statements that takes a long time to ensure that mysqld are using indexes properly. *Note Explain::. You should also test complicated queries that didn't complete within the `mysql' command line tool. If you find the text `mysqld restarted' in the error log file (normally named `hostname.err') you have probably found a query that causes `mysqld' to fail. If this happens you should check all your tables with `isamchk' (*note Maintenance::.), and test the queries in the *MySQL* log files if someone doesn't work. If you find such a query, try first upgrading to the newest *MySQL* version. If this doesn't help and you can't find anything in the `mysql' mail archive, you should report the bug to . Links to mail archives are available at the online *MySQL* documentation page (http://www.tcx.se/doc.html). If you get corrupted tables or if `mysqld' always fails after some update commands, you can test if this bug is reproducible by doing the following: * Stop the mysqld daemon (with `mysqladmin shutdown') * Check all tables with `isamchk -s database/*.ISM'. Repair any wrong tables with `isamchk -r database/table.ISM'. * Start `mysqld' with `--log-update' * When you have got a crashed table, stop the `mysqld server'. * Restore the backup. * Restart the `mysqld' server *without* `--log-update' * Re-execute the commands with `mysql < update-log'. The update log is saved in the *MySQL* database directory with the name `your-hostname.#'. * If the tables are now again corrupted, you have found reproducible bug in the `ISAM' code! ftp the tables + the update log to `ftp://www.tcx.se/pub/mysql/secret' and we will fix this as soon as possible! The command `mysqladmin debug' will dump some information about locks in use, used memory and query usage to the mysql log file. This may help solve some problems. This command also provides some usefull information even if you haven't compiled *MySQL* for debugging! If the problem is that some tables are getting slower and slower you should try to repair the tables with `isamchk' to optimize the table layout. You should also check the slow queries with `EXPLAIN'. *Note Maintenance::. You should also read the OS-specific section in this manual for problems that may be unique to your environment. *Note System-specifics:: Comments about RTS threads ========================== I have tried to use the RTS thread packages with *MySQL* but stumbled on the following problems: They use old version of a lot of POSIX calls and it is very tedious to make wrappers for all functions. I am inclined to think that it would be easier to change the thread libraries to the newest POSIX specification. Some wrappers are already written. See `mysys/my_pthread.c' for more info. At least the following should be changed: `pthread_get_specific' should use one argument. `sigwait' should take two arguments. A lot of functions (at least `pthread_cond_wait', `pthread_cond_timedwait') should return the error code on error. Now they return -1 and set `errno'. Another problem is that user-level threads use the `ALRM' signal and this aborts a lot of functions (`read', `write', `open'...). *MySQL* should do a retry on interrupt on all of these but it is not that easy to verify it. The biggest unsolved problem is the following: To get thread-level alarms I changed `mysys/thr_alarm.c' to wait between alarms with `pthread_cond_timedwait()', but this aborts with error `EINTR'. I tried to debug the thread library as to why this happens, but couldn't find any easy solution. If someone wants to try *MySQL* with RTS threads I suggest the following: * Change functions *MySQL* uses from the thread library to POSIX. This shouldn't take that long. * Compile all libraries with the `-DHAVE_rts_threads'. * Compile `thr_alarm'. * If there are some small differences in the implementation, they may be fixed by changing `my_pthread.h' and `my_pthread.c'. * Run `thr_alarm'. If it runs without any "warning", "error" or aborted messages, you are on the right track. Here follows a successful run on Solaris: Main thread: 1 Tread 0 (5) started Thread: 5 Waiting process_alarm Tread 1 (6) started Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 1 (1) sec Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 2 (2) sec Thread: 6 Simulation of no alarm needed Thread: 6 Slept for 0 (3) sec Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 4 (4) sec Thread: 6 Waiting process_alarm thread_alarm Thread: 5 Slept for 10 (10) sec Thread: 5 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 5 (5) sec Thread: 6 Waiting process_alarm process_alarm ... thread_alarm Thread: 5 Slept for 0 (1) sec end Differences between different thread packages ============================================= *MySQL* is very dependent on the thread package used. So when choosing a good platform for *MySQL*, the thread package is very important. There are at least three types of thread packages: * User threads in a single process. Thread switching is managed with alarms and the threads library manages all non-thread-safe functions with locks. Read, write and select operations are usually managed with a thread-specific select that switches to another thread if the running threads have to wait for data. If the user thread packages are integrated in the standard libs (FreeBSD and BSDI threads) the thread package requires less overhead than thread packages that have to map all unsafe calls (MIT-pthreads, FSU-threads and RTS threads). In some environments (for example, SCO), all system calls are thread-safe so the mapping can be done very easily (FSU-threads on SCO). Downside: All mapped calls take a little time and it's quite tricky to be able to handle all situations. There are usually also some system calls that are not handled by the thread package (like MIT-pthreads and sockets). Thread scheduling isn't always optimal. * User threads in separate processes. Thread switching is done by the kernel and all data are shared between threads. The thread package manages the standard thread calls to allow sharing data between threads. LinuxThreads is using this method. Downside: Lots of processes. Thread creating is slow. If one thread dies the rest are usually left hanging and you must kill them all before restarting. Thread switching is somewhat expensive. * Kernel threads. Thread switching is handled by the thread library or the kernel and is very fast. Everything is done in one process, but on some systems, `ps' may show the different threads. If one thread aborts the whole process aborts. Most system calls are thread-safe and should require very little overhead. Solaris, HP-UX, AIX and OSF1 have kernel threads. In some systems kernel threads are managed by integrating user level threads in the system libraries. In such cases, the thread switching can only be done by the thread library and the kernel isn't really "thread aware". Description of *MySQL* regular expression syntax ************************************************ A regular expression (regex) is a powerful way of specifying a complex search. *MySQL* uses regular Henry Spencer's inplementation of regular expressions. And that is aimed to conform to POSIX 1003.2. *MySQL* uses the extended version. This is a simplistic reference that skips the details. To get more exact information, see Henry Spencer's `regex(7)' manual page that is included in the source distribution. *Note Credits::. A regular expression describes a set of strings. The simplest regexp is one that has no special characters in it. For example, the regexp `hello' matches `hello' and nothing else. Nontrivial regular expressions use certain special constructs so that they can match more than one string. For example, the regexp `hello|word' matches either the string `hello' or the string `word'. As a more complex example, the regexp `B[an]*s' matches any of the strings `Bananas', `Baaaaas', `Bs' and any other string starting with a `B', ending with an `s', and containing any number of `a' or `n' characters in between. A regular expression may use any of the following special characters/constructs: `^' Match the beginning of a string. mysql> select "fo\nfo" REGEXP "^fo$"; -> 0 mysql> select "fofo" REGEXP "^fo"; -> 1 `$' Match the end of a string. mysql> select "fo\no" REGEXP "^fo\no$"; -> 1 mysql> select "fo\no" REGEXP "^fo$"; -> 0 `.' Match any character (including newline). mysql> select "fofo" REGEXP "^f.*"; -> 1 mysql> select "fo\nfo" REGEXP "^f.*"; -> 1 `a*' Match any sequence of zero or more `a' characters. mysql> select "Ban" REGEXP "^Ba*n"; -> 1 mysql> select "Baaan" REGEXP "^Ba*n"; -> 1 mysql> select "Bn" REGEXP "^Ba*n"; -> 1 `a+' Match any sequence of one or more `a' characters. mysql> select "Ban" REGEXP "^Ba+n"; -> 1 mysql> select "Bn" REGEXP "^Ba+n"; -> 0 `a?' Match either zero or one `a' character. mysql> select "Bn" REGEXP "^Ba?n"; -> 1 mysql> select "Ban" REGEXP "^Ba?n"; -> 1 mysql> select "Baan" REGEXP "^Ba?n"; -> 0 `de|abc' Match either of the sequences `de' or `abc'. mysql> select "pi" REGEXP "pi|apa"; -> 1 mysql> select "axe" REGEXP "pi|apa"; -> 0 mysql> select "apa" REGEXP "pi|apa"; -> 1 mysql> select "apa" REGEXP "^(pi|apa)$"; -> 1 mysql> select "pi" REGEXP "^(pi|apa)$"; -> 1 mysql> select "pix" REGEXP "^(pi|apa)$"; -> 0 `(abc)*' Match zero or more instances of the sequence `abc'. mysql> select "pi" REGEXP "^(pi)+$"; -> 1 mysql> select "pip" REGEXP "^(pi)+$"; -> 0 mysql> select "pipi" REGEXP "^(pi)+$"; -> 1 `{1}' `{2,3}' The is a more general way of writing regexps that match many occurrences of the previous atam. `a*' Can be written as `a{0,}'. `a+' Can be written as `a{1,}'. `a?' Can be written as `a{0,1}'. To be more precise, an atom followed by a bound containing one integer `i' and no comma matches a sequence of exactly `i' matches of the atom. An atom followed by a bound containing one integer `i' and a comma matches a sequence of `i' or more matches of the atom. An atom followed by a bound containing two integers `i' and `j' matches a sequence of `i' through `j' (inclusive) matches of the atom. Both arguments must `0 >= value <= RE_DUP_MAX (default 255)'. If there are two arguments, the second must be greater than or equal to the first. `[a-dX]' `[^a-dX]' Matches any character which is (or is not, if ^ is used) either `a', `b', `c', `d' or `X'. To include a literal `]' character, it must immediately follow the opening bracket `['. To include a literal `-' character, it must be written first or last. So `[0-9]' matches any decimal digit. Any character that does not have a defined meaning inside a `[]' pair has no special meaning and matches only itself. mysql> select "aXbc" REGEXP "[a-dXYZ]"; -> 1 mysql> select "aXbc" REGEXP "^[a-dXYZ]$"; -> 0 mysql> select "aXbc" REGEXP "^[a-dXYZ]+$"; -> 1 mysql> select "aXbc" REGEXP "^[^a-dXYZ]+$"; -> 0 mysql> select "gheis" REGEXP "^[^a-dXYZ]+$"; -> 1 mysql> select "gheisa" REGEXP "^[^a-dXYZ]+$"; -> 0 `[[.characters.]]' The sequence of characters of that collating element. The sequence is a single element of the bracket expression's list. A bracket expression containing a multi-character collating element can thus match more than one character, e.g., if the collating sequence includes a `ch' collating element, then the regular expression `[[.ch.]]*c' matches the first five characters of `chchcc'. `[=character-class=]' An equivalence class, standing for the sequences of characters of all collating elements equivalent to that one, including itself. For example, if `o' and `(+)' are the members of an equivalence class, then `[[=o=]]', `[[=(+)=]]', and `[o(+)]' are all synonymous. An equivalence class may not be an endpoint of a range. `[:character_class:]' Within a bracket expression, the name of a character class enclosed in `[:' and `:]' stands for the list of all characters belonging to that class. Standard character class names are: alnum digit punct alpha graph space blank lower upper cntrl print xdigit These stand for the character classes defined in the `ctype(3)' manual page. A locale may provide others. A character class may not be used as an endpoint of a range. mysql> select "justalnums" REGEXP "[[:alnum:]]+"; -> 1 mysql> select "!!" REGEXP "[[:alnum:]]+"; -> 0 `[[:<:]]' `[[:>:]]' These match the null string at the beginning and end of a word respectively. A word is defined as a sequence of word characters which is neither preceded nor followed by word characters. A word character is an alnum character (as defined by `ctype(3)') or an underscore (`_'). mysql> select "a word a" REGEXP "[[:<:]]word[[:>:]]"; -> 1 mysql> select "a xword a" REGEXP "[[:<:]]word[[:>:]]"; -> 0 mysql> select "weeknights" REGEXP "^(wee|week)(knights|nights)$"; -> 1 What is Unireg? *************** Unireg is our tty interface builder, but it uses a low level connection to our NISAM (which is used by *MySQL*) and because of this it is very quick. It has existed since 1979 (on Unix in C since ~1986). Unireg has the following components: * One table viewer with updates/browsing. * Multi table viewer (with one scrolling region). * Table creator. (With lots of column tags you can't create with *MySQL*) This is WYSIWYG (for a tty). You design a screen and Unireg prompts for the column specification. * Report generator. * A lot of utilities (quick export/import of tables to/from text files, analysis of table contents...). * Powerful multi-table updates (which we use a lot) with a BASIC like language with LOTS of functions. * Dynamic languages (at present in Swedish and Finnish). If somebody wants an English version there are a few files that would have to be translated. * The ability to run updates interactively or in a batch. * Emacs-like key definitions with keyboard macros. * All this in a binary of 800k. * The `convform' utility. Changes `.frm' and text files between different character sets. * The `pack_isam' utility. Packs a NISAM table (makes it 50-80% smaller). The table can be read by *MySQL* like an ordinary table. Only one record has to be decompressed per access. Cannot handle `BLOB' columns or updates (yet). We update most of our production databases with the Unireg interface and serve web pages through *MySQL* (and in some extreme cases the Unireg report generator). Unireg takes about 3M of disk space and works on at least the following platforms: SUN OS 4.x, Solaris, Linux, HP-UX, ICL Unix, DNIX, SCO and MSDOS. Unireg is currently only available in Swedish and Finnish. The price tag for Unireg is 10,000 Swedish kr (about $1500 US), but this includes support. Unireg is distributed as a binary. (But all the ISAM sources can be found in *MySQL*). Usually we compile the binary for the customer at their site. All new development is concentrated to *MySQL*. The *MySQL* server license for non Microsoft operating systems ************************************************************** *MySQL FREE PUBLIC LICENSE* (Version 4, March 5, 1995) Copyright (C) 1995, 1996 TcX AB & Monty Program KB & Detron HB Stockholm SWEDEN, Helsingfors FINLAND and Uppsala SWEDEN All rights reserved. NOTE: This license is not the same as any of the GNU Licenses published by the Free Software Foundation. Its terms are substantially different from those of the GNU Licenses. If you are familiar with the GNU Licenses, please read this license with extra care. This License applies to the computer program known as "MySQL". The "Program", below, refers to such program, and a "work based on the Program" means either the Program or any derivative work of the Program, as defined in the United States Copyright Act of 1976, such as a translation or a modification. The Program is a copyrighted work whose copyright is held by TcX Datakonsult AB and Monty Program KB and Detron HB. This License does not apply when running "MySQL" on any Microsoft operating system. Microsoft operating systems include all versions of Microsoft Windows NT and Microsoft Windows. BY MODIFYING OR DISTRIBUTING THE PROGRAM (OR ANY WORK BASED ON THE PROGRAM), YOU INDICATE YOUR ACCEPTANCE OF THIS LICENSE TO DO SO, AND ALL ITS TERMS AND CONDITIONS FOR COPYING, DISTRIBUTING OR MODIFYING THE PROGRAM OR WORKS BASED ON IT. NOTHING OTHER THAN THIS LICENSE GRANTS YOU PERMISSION TO MODIFY OR DISTRIBUTE THE PROGRAM OR ITS DERIVATIVE WORKS. THESE ACTIONS ARE PROHIBITED BY LAW. IF YOU DO NOT ACCEPT THESE TERMS AND CONDITIONS, DO NOT MODIFY OR DISTRIBUTE THE PROGRAM. 1. Licenses. Licensor hereby grants you the following rights, provided that you comply with all of the restrictions set forth in this License and provided, further, that you distribute an unmodified copy of this License with the Program: a. You may copy and distribute literal (i.e., verbatim) copies of the Program's source code as you receive it throughout the world, in any medium. b. You may modify the Program, create works based on the Program and distribute copies of such throughout the world, in any medium. 2. Restrictions. This license is subject to the following restrictions: a. Distribution of the Program or any work based on the Program by a commercial organization to any third party is prohibited if any payment is made in connection with such distribution, whether directly (as in payment for a copy of the Program) or indirectly (as in payment for some service related to the Program, or payment for some product or service that includes a copy of the Program "without charge"; these are only examples, and not an exhaustive enumeration of prohibited activities). However, the following methods of distribution involving payment shall not in and of themselves be a violation of this restriction: A. Posting the Program on a public access information storage and retrieval service for which a fee is received for retrieving information (such as an on-line service), provided that the fee is not content-dependent (i.e., the fee would be the same for retrieving the same volume of information consisting of random data). B. Distributing the Program on a CD-ROM, provided that the files containing the Program are reproduced entirely and verbatim on such CD-ROM, and provided further that all information on such CD-ROM be redistributable for non-commercial purposes without charge. b. Activities other than copying, distribution and modification of the Program are not subject to this License and they are outside its scope. Functional use (running) of the Program is not restricted, and any output produced through the use of the Program is subject to this license only if its contents constitute a work based on the Program (independent of having been made by running the Program). c. You must meet all of the following conditions with respect to the distribution of any work based on the Program: A. If you have modified the Program, you must cause your work to carry prominent notices stating that you have modified the Program's files and the date of any change; B. You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole and at no charge to all third parties under the terms of this License; C. If the modified program normally reads commands interactively when run, you must cause it, at each time the modified program commences operation, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty). Such notice must also state that users may redistribute the Program only under the conditions of this License and tell the user how to view the copy of this License included with the Program. (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.); D. You must accompany any such work based on the Program with the complete corresponding machine-readable source code, delivered on a medium customarily used for software interchange. The source code for a work means the preferred form of the work for making modifications to it. For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable code. However, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable code; E. If you distribute any written or printed material at all with the Program or any work based on the Program, such material must include either a written copy of this License, or a prominent written indication that the Program or the work based on the Program is covered by this License and written instructions for printing and/or displaying the copy of the License on the distribution medium; F. You may not impose any further restrictions on the recipient's exercise of the rights granted herein. If distribution of executable or object code is made by offering the equivalent ability to copy from a designated place, then offering equivalent ability to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source code along with the object code. 3. Reservation of Rights. No rights are granted to the Program except as expressly set forth herein. You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance. 4. Other Restrictions. If the distribution and/or use of the Program is restricted in certain countries for any reason, Licensor may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License. 5. Limitations. THE PROGRAM IS PROVIDED TO YOU "AS IS," WITHOUT WARRANTY. THERE IS NO WARRANTY FOR THE PROGRAM, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF THIRD PARTY RIGHTS. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL LICENSOR, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. The *MySQL* license for Microsoft operating systems *************************************************** *MySQL shareware license for Microsoft operating systems* (Version 1, September 4, 1998) Copyright (C) 1998 TcX AB & Monty Program KB & Detron HB Stockholm SWEDEN, Helsingfors FINLAND and Uppsala SWEDEN All rights reserved. This License applies to the computer program known as "MySQL". This License applies when running MySQL on any Microsoft operating system. Microsoft operating systems include all versions of Microsoft Windows NT and Microsoft Windows. YOU SHOULD CAREFULLY READ THE FOLLOWING TERMS AND CONDITIONS BEFORE USING, COPYING OR DISTRIBUTING MySQL. BY USING, COPYING AND DISTRIBUTING MySQL, YOU INDICATE YOUR ACCEPTANCE OF THIS LICENSE TO DO SO, AND ALL ITS TERMS AND CONDITIONS FOR USING, COPYING AND DISTRIBUTING MySQL OR WORKS BASED ON IT. NOTHING OTHER THAN THIS LICENSE GRANTS YOU PERMISSION TO USE, COPY OR DISTRIBUTE MySQL OR ITS DERIVATIVE WORKS. THESE ACTIONS ARE PROHIBITED BY LAW. IF YOU DO NOT ACCEPT THESE TERMS AND CONDITIONS, DO NOT USE, COPY OR DISTRIBUTE MySQL. 1. Evaluation and License Registration. This is an evaluation version of MySQL for Win32. Subject to the terms below, you are hereby licensed to use MySQL for evaluation purposes without charge for a period of 30 days. If you use MySQL after the 30 day evaluation period the registration and purchase of a MySQL license is required. The price for a MySQL license is currently $200 and email support starts from $200/year. Quantity discounts are available. If you pay by credit card, the currency is FIM (Finish Marks) so the prices will differ slightly. The easiest way to register or find options about how to pay for MySQL is to use the license form at TcX's secure server at `https://www.tcx.se/license.htmy'. This can be used also when paying with credit card over the Internet. Other applicables for paying are SWIFT payments, cheques and credit cards. Payment should be made to: Postgirot Bank AB 105 06 STOCKHOLM, SWEDEN T.C.X DataKonsult AB BOX 6434 11382 STOCKHOLM, SWEDEN SWIFT address: PGSI SESS Account number: 96 77 06 - 3 Specify: license(/support) and your name and email address. In Europe and Japan, EuroGiro (that should be cheaper) can be used to the same account. If you want to pay by cheque make it payable to "Monty Program KB" and mail it to the address below. T.C.X DataKonsult AB BOX 6434 11382 STOCKHOLM, SWEDEN For more information about commercial licensing, please contact: David Axmark Kungsgatan 65 B 753 21 UPPSALA SWEDEN Voice Phone +46-18-10 22 80 (Swedish and English spoken) Fax +46-8-729 69 05 (Email *much* preferred) E-Mail: mysql-licensing@tcx.se For more about the license prices and commercial supports, like e-mail supports, please refer to the MySQL manual. *Note Cost::. *Note Support::. The use of MySQL or any work based on MySQL after the 30-day evaluation period is in violation of international copyright laws. 2. Registered version of MySQL. After you have purcased a MySQL license we will send you a receipt by snail mail. You are allowed to use MySQL or any work based on MySQL after the 30-days evaluation period. The use of MySQL is, however, restricted to one physical computer, but there are no restrictions on concurrent uses of MySQL or the number of MySQL servers run on the computer. We will also e-mail you an address and password for a password-protected WWW page that always has the newest MySQL - Win32 version. Our current policy is that a user with the MySQL license can get free upgrades. The best way to ensure that you get the best possible support is to purcase commercial support! 3. Registration for use in education and university or government-sponsored research. You may obtain a MySQL license for the use in education and university or government-sponsored research for free. In that case, send a detailed application for licensing MySQL for such use to the email address . The following information is required in the application: * the name of the school or institute. * a short description of the school or institute and of the type of education, resarch or other functions it provides. * a detailed report of the use of MySQL in the institution. In this case you will be provided with a license that entitles you to use MySQL in a specified manner. 4. Distribution. Provided that you verify that you are distributing an evaluation or educational/research version of MySQL you are hereby licensed to make as many literal (i.e., verbatim) copies of the evaluation version of MySQL and documentation as you wish. 5. Restrictions. The client code of MySQL is in the Public Domain or under the GPL (for example the code for readline) license. You are not allowed to modify, recompile, translate or create derivative works based upon any part of the server code of MySQL. 6. Reservation of Rights. No rights are granted to MySQL except as expressly set forth herein. You may not copy or distribute MySQL except as expressly provided under this License. Any attempt otherwise to copy or distribute MySQL is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance. 7. Other Restrictions. If the distribution and/or use of MySQL is restricted in certain countries for any reason, the Licensor may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License. 8. Limitations. MySQL IS PROVIDED TO YOU "AS IS," WITHOUT WARRANTY. THERE IS NO WARRANTY FOR MySQL, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF THIRD PARTY RIGHTS. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF MySQL IS WITH YOU. SHOULD MySQL PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL THE LICENSOR, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE MySQL AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE MySQL (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF MySQL TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SQL command, type and function index ************************************ * Menu: * ! (logical NOT): Logical functions. * != (not equal): Comparison functions. * % (modulo): Mathematical functions. * % (wildcard character): Base Syntax. * & (bitwise AND): Bit functions. * && (logical AND): Logical functions. * () (parentheses): Grouping functions. * * (multiplication): Arithmetic functions. * + (addition): Arithmetic functions. * - (minus): Mathematical functions. * - (subtraction): Arithmetic functions. * .my.cnf file <1>: Access denied. * .my.cnf file <2>: Connecting. * .my.cnf file <3>: Option files. * .my.cnf file <4>: Multiple servers. * .my.cnf file: Win32. * .mysql_history file: Programs. * .pid file: Maintenance regime. * / (division): Arithmetic functions. * < (less than): Comparison functions. * << (left shift): Bit functions. * <= (less than or equal): Comparison functions. * <> (not equal): Comparison functions. * = (equal): Comparison functions. * > (greater than): Comparison functions. * >= (greater than or equal): Comparison functions. * >> (right shift): Bit functions. * \" (double quote): Base Syntax. * \' (single quote): Base Syntax. * \0 (ASCII 0): Base Syntax. * \\ (escape): Base Syntax. * \b (backspace): Base Syntax. * \n (newline): Base Syntax. * \r (carriage return): Base Syntax. * \t (tab): Base Syntax. * _ (wildcard character): Base Syntax. * ABS(): Mathematical functions. * ACOS(): Mathematical functions. * ADDDATE(): Date and time functions. * addition (+): Arithmetic functions. * alias: Problems with NULL. * ALTER TABLE: Create table. * AND, bitwise: Bit functions. * AND, logical: Logical functions. * Arithmetic functions: Arithmetic functions. * ASCII(): String functions. * ASIN(): Mathematical functions. * ATAN(): Mathematical functions. * ATAN2(): Mathematical functions. * AUTO_INCREMENT, and NULL values: Problems with NULL. * AVG(): Group by functions. * backspace (\b): Base Syntax. * BETWEEN ... AND: Comparison functions. * BIGINT: Column types. * BIN(): String functions. * Bit functions: Arithmetic functions. * BIT_AND(): Group by functions. * BIT_COUNT(): Bit functions. * BIT_OR(): Group by functions. * BLOB <1>: String types. * BLOB: Column types. * carriage return (\r): Base Syntax. * CC environment variable <1>: configure options. * CC environment variable: Compilation problems. * CEILING(): Mathematical functions. * CFLAGS environment variable: Compilation problems. * CHAR <1>: Column types. * CHAR: String types. * CHAR(): String functions. * CHAR_LENGTH(): String functions. * CHARACTER_LENGTH(): String functions. * ChopBlanks: Perl DBI Class. * Comment syntax: Drop index. * Comparison operators: Logical functions. * CONCAT(): String functions. * connect(): Perl DBI Class. * Control flow functions: String comparison functions. * CONV(): String functions. * COS(): Mathematical functions. * COT(): Mathematical functions. * COUNT(): Group by functions. * CREATE DATABASE: Group by functions. * CREATE FUNCTION: Comments. * CREATE INDEX: Grant. * CREATE TABLE: Drop database. * CROSS JOIN: Select. * CURDATE(): Date and time functions. * CURRENT_DATE: Date and time functions. * CURRENT_TIME: Date and time functions. * CURRENT_TIMESTAMP: Date and time functions. * CURTIME(): Date and time functions. * CXX environment variable <1>: Compilation problems. * CXX environment variable <2>: configure options. * CXX environment variable: Compilation problems. * CXXFLAGS environment variable <1>: configure options. * CXXFLAGS environment variable: Compilation problems. * data_sources(): Perl DBI Class. * DATABASE(): Miscellaneous functions. * DATE <1>: Column types. * DATE: Date and time types. * Date and time functions: String functions. * DATE_ADD(): Date and time functions. * DATE_FORMAT(): Date and time functions. * DATE_SUB(): Date and time functions. * DATETIME <1>: Date and time types. * DATETIME: Column types. * DAYNAME(): Date and time functions. * DAYOFMONTH(): Date and time functions. * DAYOFWEEK(): Date and time functions. * DAYOFYEAR(): Date and time functions. * DBI->connect(): Perl DBI Class. * DBI->data_sources(): Perl DBI Class. * DBI->disconnect: Perl DBI Class. * DBI->do(): Perl DBI Class. * DBI->execute: Perl DBI Class. * DBI->fetchall_arrayref: Perl DBI Class. * DBI->fetchrow_array: Perl DBI Class. * DBI->fetchrow_arrayref: Perl DBI Class. * DBI->fetchrow_hashref: Perl DBI Class. * DBI->finish: Perl DBI Class. * DBI->prepare(): Perl DBI Class. * DBI->quote: Base Syntax. * DBI->quote(): Perl DBI Class. * DBI->rows: Perl DBI Class. * DBI->{ChopBlanks}: Perl DBI Class. * DBI->{insertid}: Perl DBI Class. * DBI->{is_blob}: Perl DBI Class. * DBI->{is_key}: Perl DBI Class. * DBI->{is_not_null}: Perl DBI Class. * DBI->{is_num}: Perl DBI Class. * DBI->{is_pri_key}: Perl DBI Class. * DBI->{length}: Perl DBI Class. * DBI->{max_length}: Perl DBI Class. * DBI->{NAME}: Perl DBI Class. * DBI->{NULLABLE}: Perl DBI Class. * DBI->{NUM_OF_FIELDS}: Perl DBI Class. * DBI->{table}: Perl DBI Class. * DBI->{type}: Perl DBI Class. * DECIMAL: Column types. * DEGREES(): Mathematical functions. * DELETE: Drop table. * DESC: Explain. * DESCRIBE: Explain. * disconnect: Perl DBI Class. * division (/): Arithmetic functions. * do(): Perl DBI Class. * DOUBLE: Column types. * DOUBLE PRECISION: Column types. * double quote (\"): Base Syntax. * DROP DATABASE: Create database. * DROP FUNCTION: Comments. * DROP INDEX: Create index. * DROP TABLE: Optimize table. * ELT(): String functions. * ENCRYPT(): Miscellaneous functions. * ENUM <1>: Column types. * ENUM: String types. * Environment variable, CC <1>: configure options. * Environment variable, CC: Compilation problems. * Environment variable, CFLAGS: Compilation problems. * Environment variable, CXX <1>: Compilation problems. * Environment variable, CXX <2>: configure options. * Environment variable, CXX: Compilation problems. * Environment variable, CXXFLAGS <1>: configure options. * Environment variable, CXXFLAGS: Compilation problems. * Environment variable, HOME: Programs. * Environment variable, LOGIN: Connecting. * Environment variable, LOGNAME: Connecting. * Environment variable, MYSQL_DEBUG <1>: Programs. * Environment variable, MYSQL_DEBUG: Compilation problems. * Environment variable, MYSQL_HISTFILE: Programs. * Environment variable, MYSQL_HOST: Connecting. * Environment variable, MYSQL_PWD <1>: Connecting. * Environment variable, MYSQL_PWD: Programs. * Environment variable, MYSQL_TCP_PORT <1>: mysql_install_db. * Environment variable, MYSQL_TCP_PORT <2>: Multiple servers. * Environment variable, MYSQL_TCP_PORT: Programs. * Environment variable, MYSQL_UNIX_PORT <1>: mysql_install_db. * Environment variable, MYSQL_UNIX_PORT <2>: Programs. * Environment variable, MYSQL_UNIX_PORT <3>: mysql_install_db. * Environment variable, MYSQL_UNIX_PORT: Multiple servers. * Environment variable, PATH: Installing binary. * Environment variable, TMPDIR: mysql_install_db. * Environment variable, USER: Connecting. * Environment variables, CXX: Compilation problems. * equal (=): Comparison functions. * escape (\\): Base Syntax. * execute: Perl DBI Class. * EXP(): Mathematical functions. * EXPLAIN: Show. * fetchall_arrayref: Perl DBI Class. * fetchrow_array: Perl DBI Class. * fetchrow_arrayref: Perl DBI Class. * fetchrow_hashref: Perl DBI Class. * FIELD(): String functions. * FIND_IN_SET(): String functions. * finish: Perl DBI Class. * FLOAT: Column types. * FLOAT(4): Column types. * FLOAT(8): Column types. * FLOAT(M,D): Column types. * FLOOR(): Mathematical functions. * FORMAT(): Miscellaneous functions. * FROM_DAYS(): Date and time functions. * FROM_UNIXTIME(): Date and time functions. * Functions, arithmetic: Arithmetic functions. * Functions, bit: Arithmetic functions. * Functions, control flow: String comparison functions. * Functions, date and time: String functions. * Functions, GROUP BY: Miscellaneous functions. * Functions, logical: Bit functions. * Functions, mathematical: Control flow functions. * Functions, miscellaneous: Date and time functions. * Functions, string: Mathematical functions. * Functions, string comparison: Comparison functions. * Functions, user-defined: Comments. * GET_LOCK(): Miscellaneous functions. * GRANT: Set option. * greater than (>): Comparison functions. * greater than or equal (>=): Comparison functions. * GREATEST(): Mathematical functions. * GROUP BY functions: Miscellaneous functions. * HEX(): String functions. * HOME environment variable: Programs. * host.frm, problems finding: Post-installation. * HOUR(): Date and time functions. * IF(): Control flow functions. * IFNULL(): Control flow functions. * IN: Comparison functions. * INSERT: Join. * INSERT(): String functions. * insertid: Perl DBI Class. * INSTR(): String functions. * INT: Column types. * INTEGER: Column types. * INTERVAL(): Comparison functions. * is_blob: Perl DBI Class. * is_key: Perl DBI Class. * is_not_null: Perl DBI Class. * is_num: Perl DBI Class. * is_pri_key: Perl DBI Class. * ISNULL(): Comparison functions. * JOIN: Select. * LAST_INSERT_ID(): Commit-rollback. * LAST_INSERT_ID([expr]): Miscellaneous functions. * LCASE(): String functions. * LEAST(): Mathematical functions. * LEFT JOIN: Select. * LEFT OUTER JOIN: Select. * LEFT(): String functions. * length: Perl DBI Class. * LENGTH(): String functions. * less than (<): Comparison functions. * less than or equal (<=): Comparison functions. * LIKE: String comparison functions. * LIKE, and indexes: MySQL indexes. * LIKE, and wildcards: MySQL indexes. * LOAD DATA INFILE <1>: Replace. * LOAD DATA INFILE: Problems with NULL. * LOCATE(): String functions. * LOCK TABLES: Describe. * LOG(): Mathematical functions. * LOG10(): Mathematical functions. * Logical functions: Bit functions. * LOGIN environment variable: Connecting. * LOGNAME environment variable: Connecting. * LONGBLOB: Column types. * LONGTEXT: Column types. * LOWER(): String functions. * LPAD(): String functions. * LTRIM(): String functions. * MAKE_SET(): String functions. * Mathematical functions: Control flow functions. * MAX(): Group by functions. * max_length: Perl DBI Class. * MEDIUMBLOB: Column types. * MEDIUMINT: Column types. * MEDIUMTEXT: Column types. * MID(): String functions. * MIN(): Group by functions. * minus (-): Mathematical functions. * MINUTE(): Date and time functions. * Miscellaneous functions: Date and time functions. * MOD(): Mathematical functions. * modulo (%): Mathematical functions. * MONTH(): Date and time functions. * MONTHNAME(): Date and time functions. * multiplication (*): Arithmetic functions. * mysql_affected_rows(): C API functions. * mysql_close(): C API functions. * mysql_connect(): C API functions. * mysql_create_db(): C API functions. * mysql_data_seek(): C API functions. * MYSQL_DEBUG environment variable <1>: Programs. * MYSQL_DEBUG environment variable: Compilation problems. * mysql_debug(): C API functions. * mysql_drop_db(): C API functions. * mysql_dump_debug_info(): C API functions. * mysql_eof(): C API functions. * mysql_errno(): C API functions. * mysql_error(): C API functions. * mysql_escape_string() <1>: C API functions. * mysql_escape_string(): Base Syntax. * mysql_fetch_field(): C API functions. * mysql_fetch_field_direct(): C API functions. * mysql_fetch_fields(): C API functions. * mysql_fetch_lengths(): C API functions. * mysql_fetch_row(): C API functions. * mysql_field_seek(): C API functions. * mysql_field_tell(): C API functions. * mysql_free_result(): C API functions. * mysql_get_client_info(): C API functions. * mysql_get_host_info(): C API functions. * mysql_get_proto_info(): C API functions. * mysql_get_server_info(): C API functions. * MYSQL_HISTFILE environment variable: Programs. * MYSQL_HOST environment variable: Connecting. * mysql_info() <1>: Insert. * mysql_info() <2>: Load. * mysql_info() <3>: Alter table. * mysql_info() <4>: Update. * mysql_info(): C API functions. * mysql_init(): C API functions. * mysql_insert_id() <1>: Commit-rollback. * mysql_insert_id(): C API functions. * mysql_kill(): C API functions. * mysql_list_dbs(): C API functions. * mysql_list_fields(): C API functions. * mysql_list_processes(): C API functions. * mysql_list_tables(): C API functions. * mysql_num_fields(): C API functions. * mysql_num_rows(): C API functions. * mysql_ping(): C API functions. * MYSQL_PWD environment variable <1>: Programs. * MYSQL_PWD environment variable: Connecting. * mysql_query(): C API functions. * mysql_real_connect(): C API functions. * mysql_real_query(): C API functions. * mysql_reload(): C API functions. * mysql_row_tell(): C API functions. * mysql_select_db(): C API functions. * mysql_shutdown(): C API functions. * mysql_stat(): C API functions. * mysql_store_result(): C API functions. * MYSQL_TCP_PORT environment variable <1>: mysql_install_db. * MYSQL_TCP_PORT environment variable <2>: Programs. * MYSQL_TCP_PORT environment variable: Multiple servers. * mysql_thread_id(): C API functions. * MYSQL_UNIX_PORT environment variable <1>: mysql_install_db. * MYSQL_UNIX_PORT environment variable <2>: Programs. * MYSQL_UNIX_PORT environment variable: Multiple servers. * mysql_use_result(): C API functions. * NAME: Perl DBI Class. * NATURAL LEFT JOIN: Select. * NATURAL LEFT OUTER JOIN: Select. * newline (\n): Base Syntax. * not equal (!=): Comparison functions. * not equal (<>): Comparison functions. * NOT IN: Comparison functions. * NOT LIKE: String comparison functions. * NOT REGEXP: String comparison functions. * NOT, logical: Logical functions. * NOW(): Date and time functions. * NUL: Base Syntax. * NULL <1>: Base Syntax. * NULL: Case sensitivity. * NULL value: Base Syntax. * NULL values, and AUTO_INCREMENT columns: Problems with NULL. * NULL values, and TIMESTAMP columns: Problems with NULL. * NULLABLE: Perl DBI Class. * NUM_OF_FIELDS: Perl DBI Class. * NUMERIC: Column types. * OCT(): String functions. * OCTET_LENGTH(): String functions. * OPTIMIZE TABLE: Alter table. * OR, bitwise: Bit functions. * OR, logical: Logical functions. * parentheses ( and ): Grouping functions. * PASSWORD() <1>: Ignoring user. * PASSWORD() <2>: Passwords. * PASSWORD(): Miscellaneous functions. * PATH environment variable: Installing binary. * PERIOD_ADD(): Date and time functions. * PERIOD_DIFF(): Date and time functions. * PI(): Mathematical functions. * POSITION(): String functions. * POW(): Mathematical functions. * POWER(): Mathematical functions. * prepare(): Perl DBI Class. * QUARTER(): Date and time functions. * quote(): Perl DBI Class. * RADIANS(): Mathematical functions. * RAND(): Mathematical functions. * REAL: Column types. * REGEXP: String comparison functions. * RELEASE_LOCK(): Miscellaneous functions. * REPEAT(): String functions. * REPLACE: Insert. * REPLACE(): String functions. * return (\r): Base Syntax. * REVERSE(): String functions. * REVOKE: Set option. * RIGHT(): String functions. * RLIKE: String comparison functions. * ROUND(): Mathematical functions. * rows: Perl DBI Class. * RPAD(): String functions. * RTRIM(): String functions. * SEC_TO_TIME(): Date and time functions. * SECOND(): Date and time functions. * SELECT: Delete. * SELECT, optimizing: Show. * SESSION_USER(): Miscellaneous functions. * SET <1>: String types. * SET: Column types. * SET OPTION: Lock tables. * SHOW COLUMNS: Kill. * SHOW DATABASES: Kill. * SHOW FIELDS: Kill. * SHOW INDEX: Kill. * SHOW KEYS: Kill. * SHOW PROCESSLIST: Kill. * SHOW STATUS: Kill. * SHOW TABLES: Kill. * SHOW VARIABLES: Kill. * SIGN(): Mathematical functions. * SIN(): Mathematical functions. * single quote (\'): Base Syntax. * SMALLINT: Column types. * SOUNDEX(): String functions. * SPACE(): String functions. * SQRT(): Mathematical functions. * STD(): Group by functions. * STDDEV(): Group by functions. * STRAIGHT_JOIN: Select. * STRCMP(): String comparison functions. * String comparison functions: Comparison functions. * String functions: Mathematical functions. * SUBDATE(): Date and time functions. * SUBSTRING(): String functions. * SUBSTRING_INDEX(): String functions. * subtraction (-): Arithmetic functions. * SUM(): Group by functions. * SYSDATE(): Date and time functions. * SYSTEM_USER(): Miscellaneous functions. * tab (\t): Base Syntax. * table: Perl DBI Class. * table_cache: MySQL parameters. * TAN(): Mathematical functions. * TEXT <1>: String types. * TEXT: Column types. * TIME <1>: Date and time types. * TIME: Column types. * TIME_FORMAT(): Date and time functions. * TIME_TO_SEC(): Date and time functions. * TIMESTAMP <1>: Column types. * TIMESTAMP: Date and time types. * TIMESTAMP, and NULL values: Problems with NULL. * TINYBLOB: Column types. * TINYINT: Column types. * TINYTEXT: Column types. * TMPDIR environment variable: mysql_install_db. * TO_DAYS(): Date and time functions. * TRIM(): String functions. * TRUNCATE(): Mathematical functions. * type: Perl DBI Class. * Types: Column types. * UCASE(): String functions. * UDF functions: Comments. * UNIX_TIMESTAMP(): Date and time functions. * UNLOCK TABLES: Describe. * UPDATE: Load. * UPPER(): String functions. * USE: Update. * USER environment variable: Connecting. * USER(): Miscellaneous functions. * User-defined functions: Comments. * VARCHAR <1>: String types. * VARCHAR: Column types. * VERSION(): Miscellaneous functions. * WEEK(): Date and time functions. * WEEKDAY(): Date and time functions. * wildcard character (%): Base Syntax. * wildcard character (_): Base Syntax. * YEAR <1>: Date and time types. * YEAR: Column types. * YEAR(): Date and time functions. * | (bitwise OR): Bit functions. * || (logical OR): Logical functions. Concept Index ************* * Menu: * *MySQL*: Introduction. * *MySQL* binary: Which OS. * *MySQL* mailing lists: Useful Links. * *MySQL* mailing lists, subscribing to: Useful Links. * *MySQL* mailing lists, unsubscribing from: Useful Links. * *MySQL* source: Which OS. * *MySQL* version <1>: Installing. * *MySQL* version: Manual-info. * Adding native functions: Adding UDF. * Adding user-definable functions: Adding functions. * Alias names, case sensitivity: Legal names. * anonymous user <1>: Default privileges. * anonymous user <2>: Connection access. * anonymous user: Request access. * ANSI SQL, differences from: Grant. * Arithmetic expressions: Arithmetic functions. * AUTO_INCREMENT, using with DBI: Perl DBI Class. * Backup: Replication. * Big5 Chinese character encoding: Using DATE. * Bug reports: Asking questions. * C++ compiler cannot create executables: Compilation problems. * Case sensitivity, in access checking: Privileges. * Case sensitivity, in searches: Using DATE. * Case sensitivity, of alias names: Legal names. * Case sensitivity, of column names: Legal names. * Case sensitivity, of database names <1>: Legal names. * Case sensitivity, of database names: Extensions to ANSI. * Case sensitivity, of table names <1>: Legal names. * Case sensitivity, of table names: Extensions to ANSI. * Casts: Logical functions. * cc1plus problems: Compilation problems. * Checking tables for errors: Crash recovery. * Chinese: Using DATE. * Choosing types: String types. * Choosing version: Which OS. * Client programs, building: Installing binary. * Column names, case sensitivity: Legal names. * Command line history: Programs. * Commands out of sync: Full table. * Compatibility, Oracle <1>: Group by functions. * Compatibility, Oracle <2>: Extensions to ANSI. * Compatibility, Oracle: Explain. * Compatibility, Sybase: Use. * Configuration files: Access denied. * configure, running after prior invocation: Compilation problems. * Constant table <1>: Explain. * Constant table: Where optimizations. * Copyright: Contacting us. * Cost: Licensing and Support. * Database mirroring: Update log. * Database names, case sensitivity <1>: Legal names. * Database names, case sensitivity: Extensions to ANSI. * Database replication <1>: Update log. * Database replication: Common problems. * Date and Time types: Numeric types. * db table, sorting: Request access. * default options: Automatic start. * Disk full: Cannot find table. * Downloading: Installing. * Environment variables <1>: Tools. * Environment variables <2>: Option files. * Environment variables: Access denied. * fatal signall 11: Compilation problems. * FreeBSD troubleshooting: Compilation problems. * Full disk: Cannot find table. * Functions for SELECT and WHERE clauses: Indexes. * Functions, native, adding: Adding UDF. * Functions, user-definable, adding: Adding functions. * General Information: Top. * Getting *MySQL*: Installing. * grant tables, sorting <1>: Request access. * grant tables, sorting: Connection access. * Grouping of expressions: Grouping functions. * History file: Programs. * host table, sorting: Request access. * How to pronounce *MySQL*: What-is. * Index: Grant. * Index, leftmost prefix: MySQL indexes. * Indexes: Choosing types. * Indexes, and LIKE: MySQL indexes. * Internal compiler errors: Compilation problems. * isamchk <1>: configure options. * isamchk: Programs. * Keys: Choosing types. * Keywords: Create function. * Languages support: Server. * Leftmost prefix of index: MySQL indexes. * Linking: Installing binary. * Log file, names: Backup. * make_binary_release: Programs. * Manual information: What-is. * Memory use: MySQL parameters. * Mirroring, database: Update log. * msql2mysql: Programs. * Multi-byte characters: Adding character set. * multi-part-index: Grant. * MyODBC: Adding native function. * mysql: Programs. * mysql_fix_privilege_tables: Access denied. * mysql_install_db: Programs. * mysqlaccess: Programs. * mysqladmin <1>: Create database. * mysqladmin <2>: Show. * mysqladmin <3>: Drop database. * mysqladmin <4>: Flush. * mysqladmin <5>: Use. * mysqladmin: Programs. * mysqlbug: Programs. * mysqld: Programs. * mysqldump <1>: Upgrading-to-arch. * mysqldump: Programs. * mysqlimport <1>: Programs. * mysqlimport <2>: Load. * mysqlimport: Upgrading-to-arch. * mysqlshow: Programs. * Native functions, adding: Adding UDF. * Net etiquette <1>: Mailing-list. * Net etiquette: Crashing. * NULL values vs. empty values: Case sensitivity. * ODBC: Adding native function. * optimizations: MySQL indexes. * Oracle compatibility <1>: Extensions to ANSI. * Oracle compatibility <2>: Group by functions. * Oracle compatibility: Explain. * Overview: Top. * Pack-ISAM: mysqlimport. * pack_isam: Support. * passwords, setting: Passwords. * Passwords, setting <1>: Set option. * Passwords, setting: Grant. * Paying: Support. * Performance: Table size. * Protocol mismatch: Upgrading-from-3.20. * Quoting: Base Syntax. * Quoting binary data: Base Syntax. * Quoting strings: Perl DBI Class. * Release numbers: Which OS. * replace: Programs. * Replication: Common problems. * Replication, database <1>: Common problems. * Replication, database: Update log. * Reporting bugs: Asking questions. * Reporting errors: Useful Links. * Reserved words: Create function. * Reserved words, exceptions: Create function. * row-level locking: Commit-rollback. * Running configure after prior invocation: Compilation problems. * safe_mysqld: Programs. * Server functions: Twin event. * SHOW INDEX: Explain. * Size of tables: Update log. * Solaris troubleshooting: Compilation problems. * sorting, grant tables <1>: Request access. * sorting, grant tables: Connection access. * sql_yacc.cc problems: Compilation problems. * Stability: Features. * Startup parameters: Performance. * Storage requirements: Column types. * Strings, How to escape things: Syntax. * Strings, quoting: Perl DBI Class. * Support: Cost. * Support, types: Cost. * Sybase compatibility <1>: Update. * Sybase compatibility: Use. * Symbolic links: Where optimizations. * System table: Explain. * Table cache <1>: MySQL parameters. * Table cache: Where optimizations. * Table names, case sensitivity <1>: Extensions to ANSI. * Table names, case sensitivity: Legal names. * Table size: Update log. * Table, constant <1>: Explain. * Table, constant: Where optimizations. * Table, system: Explain. * The table is full: Packet too large. * Timezone problems <1>: BSDI2. * Timezone problems: FreeBSD. * TODO: Bugs. * Troubleshooting, FreeBSD: Compilation problems. * Troubleshooting, Solaris: Compilation problems. * Type conversions: Logical functions. * Type portability: Indexes. * Types of support: Cost. * Types, Choosing: String types. * Types, Date and Time: Numeric types. * Update log: Multi-byte characters. * user table, sorting: Connection access. * User-definable functions, adding: Adding functions. * Version, Choosing: Which OS. * Version, Latest: Installing. * Virtual memory problems while compiling: Compilation problems. * Which languages *MySQL* supports: Server. * Wildcards, and LIKE: MySQL indexes. * Wildcards, in mysql.columns_priv table: Request access. * Wildcards, in mysql.db table: Request access. * Wildcards, in mysql.host table: Request access. * Wildcards, in mysql.tables_priv table: Request access. * Wildcards, in mysql.user table: Connection access. * Windows: Adding native function. * Year 2000 compliance: Stability.