MySQL 5.0 Reference Manual

MySQL is a database management system.

A database is a structured collection of data. It may be anything from a simple shopping list to a picture gallery or the vast amounts of information in a corporate network. To add, access, and process data stored in a computer database, you need a database management system such as MySQL Server. Since computers are very good at handling large amounts of data, database management systems play a central role in computing, as standalone utilities, or as parts of other applications.

MySQL is a relational database management system.

A relational database stores data in separate tables rather than putting all the data in one big storeroom. This adds speed and flexibility. The SQL part of “MySQL” stands for “Structured Query Language.” SQL is the most common standardized language used to access databases and is defined by the ANSI/ISO SQL Standard. The SQL standard has been evolving since 1986 and several versions exist. In this manual, “SQL-92” refers to the standard released in 1992, “SQL:1999” refers to the standard released in 1999, and “SQL:2003” refers to the current version of the standard. We use the phrase “the SQL standard” to mean the current version of the SQL Standard at any time.

MySQL software is Open Source.

Open Source means that it is possible for anyone to use and modify the software. Anybody can download the MySQL software from the Internet and use it without paying anything. If you wish, you may study the source code and change it to suit your needs. The MySQL software uses the GPL (GNU General Public License), http://www.fsf.org/licenses/, to define what you may and may not do with the software in different situations. If you feel uncomfortable with the GPL or need to embed MySQL code into a commercial application, you can buy a commercially licensed version from us. See the MySQL Licensing Overview for more information (http://www.mysql.com/company/legal/licensing/).

The MySQL Database Server is very fast, reliable, and easy to use.

If that is what you are looking for, you should give it a try. MySQL Server also has a practical set of features developed in close cooperation with our users. You can find a performance comparison of MySQL Server with other database managers on our benchmark page. See Section 7.1.4, “The MySQL Benchmark Suite”.

MySQL Server was originally developed to handle large databases much faster than existing solutions and has been successfully used in highly demanding production environments for several years. Although under constant development, MySQL Server today offers a rich and useful set of functions. Its connectivity, speed, and security make MySQL Server highly suited for accessing databases on the Internet.

MySQL Server works in client/server or embedded systems.

The MySQL Database Software is a client/server system that consists of a multi-threaded SQL server that supports different backends, several different client programs and libraries, administrative tools, and a wide range of application programming interfaces (APIs).

We also provide MySQL Server as an embedded multi-threaded library that you can link into your application to get a smaller, faster, easier-to-manage standalone product.

A large amount of contributed MySQL software is available.

It is very likely that your favorite application or language supports the MySQL Database Server.

MySQL 4.0 and 4.1: MySQL 4.0 in a Nutshell, and MySQL 4.1 in a Nutshell.

MySQL 5.0: MySQL 5.0 in a Nutshell.

MySQL 5.1: MySQL 5.1 in a Nutshell.

Written in C and C++.

Tested with a broad range of different compilers.

Works on many different platforms. See Section 2.4.2, “Operating Systems Supported by MySQL Community Server”.

Uses GNU Automake, Autoconf, and Libtool for portability.

The MySQL Server design is multi-layered with independent modules.

Fully multi-threaded using kernel threads. It can easily use multiple CPUs if they are available.

Provides transactional and non-transactional storage engines.

Uses very fast B-tree disk tables (MyISAM) with index compression.

Relatively easy to add other storage engines. This is useful if you want to provide an SQL interface for an in-house database.

A very fast thread-based memory allocation system.

Very fast joins using an optimized one-sweep multi-join.

In-memory hash tables, which are used as temporary tables.

SQL functions are implemented using a highly optimized class library and should be as fast as possible. Usually there is no memory allocation at all after query initialization.

The MySQL code is tested with Purify (a commercial memory leakage detector) as well as with Valgrind, a GPL tool (http://developer.kde.org/~sewardj/).

The server is available as a separate program for use in a client/server networked environment. It is also available as a library that can be embedded (linked) into standalone applications. Such applications can be used in isolation or in environments where no network is available.

Many data types: signed/unsigned integers 1, 2, 3, 4, and 8 bytes long, FLOAT, DOUBLE, CHAR, VARCHAR, TEXT, BLOB, DATE, TIME, DATETIME, TIMESTAMP, YEAR, SET, ENUM, and OpenGIS spatial types. See Chapter 10, Data Types.

Fixed-length and variable-length records.

Full operator and function support in the SELECT list and WHERE clause of queries. For example:

mysql> SELECT CONCAT(first_name, ' ', last_name)
    -> FROM citizen
    -> WHERE income/dependents > 10000 AND age > 30;

Full support for SQL GROUP BY and ORDER BY clauses. Support for group functions (COUNT(), COUNT(DISTINCT ...), AVG(), STD(), SUM(), MAX(), MIN(), and GROUP_CONCAT()).

Support for LEFT OUTER JOIN and RIGHT OUTER JOIN with both standard SQL and ODBC syntax.

Support for aliases on tables and columns as required by standard SQL.

DELETE, INSERT, REPLACE, and UPDATE return the number of rows that were changed (affected). It is possible to return the number of rows matched instead by setting a flag when connecting to the server.

The MySQL-specific SHOW statement can be used to retrieve information about databases, storage engines, tables, and indexes. MySQL 5.0 adds support for the INFORMATION_SCHEMA database, implemented according to standard SQL.

The EXPLAIN statement can be used to determine how the optimizer resolves a query.

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. See Section 8.3, “Reserved Words”.

You can refer to tables from different databases in the same statement.

A privilege and password system that is very flexible and secure, and that allows host-based verification.

Passwords are secure because all password traffic is encrypted when you connect to a server.

Handles large databases. We use MySQL Server with databases that contain 50 million records. We also know of users who use MySQL Server with 60,000 tables and about 5,000,000,000 rows.

Up to 64 indexes per table are allowed (32 before MySQL 4.1.2). Each index may consist of 1 to 16 columns or parts of columns. The maximum index width is 1000 bytes (767 for InnoDB); before MySQL 4.1.2, the limit is 500 bytes. An index may use a prefix of a column for CHAR, VARCHAR, BLOB, or TEXT column types.

Clients can connect to MySQL Server using several protocols:

MySQL client programs can be written in many languages. A client library written in C is available for clients written in C or C++, or for any language that provides C bindings.

APIs for C, C++, Eiffel, Java, Perl, PHP, Python, Ruby, and Tcl are available, allowing MySQL clients to be written in many languages. See Chapter 20, Connectors and APIs.

The Connector/ODBC (MyODBC) interface provides MySQL support for client programs that use ODBC (Open Database Connectivity) connections. For example, you can use MS Access to connect to your MySQL server. Clients can be run on Windows or Unix. MyODBC source is available. All ODBC 2.5 functions are supported, as are many others. See Section 20.1, “MySQL Connector/ODBC”.

The Connector/J interface provides MySQL support for Java client programs that use JDBC connections. Clients can be run on Windows or Unix. Connector/J source is available. See Section 20.4, “MySQL Connector/J”.

MySQL Connector/NET enables developers to easily create .NET applications that require secure, high-performance data connectivity with MySQL. It implements the required ADO.NET interfaces and integrates into ADO.NET aware tools. Developers can build applications using their choice of .NET languages. MySQL Connector/NET is a fully managed ADO.NET driver written in 100% pure C#. See Section 20.2, “MySQL Connector/NET”.

The server can provide error messages to clients in many languages. See Section 9.3, “Setting the Error Message Language”.

Full support for several different character sets, including latin1 (cp1252), german, big5, ujis, and more. For example, the Scandinavian characters “å”, “ä” and “ö” are allowed in table and column names. Unicode support is available as of MySQL 4.1.

All data is saved in the chosen character set.

Sorting and comparisons are done according to the chosen character set and collation (using latin1 and Swedish collation by default). It is possible to change this when the MySQL server is started. To see an example of very advanced sorting, look at the Czech sorting code. MySQL Server supports many different character sets that can be specified at compile time and runtime.

As of MySQL 4.1, the server time zone can be changed dynamically, and individual clients can specify their own time zone. Section 9.7, “MySQL Server Time Zone Support”.

MySQL AB provides several client and utility programs. These include both command-line programs such as mysqldump and mysqladmin, and graphical programs such as MySQL Administrator and MySQL Query Browser.

MySQL Server has built-in support for SQL statements to check, optimize, and repair tables. These statements are available from the command line through the mysqlcheck client. MySQL also includes myisamchk, a very fast command-line utility for performing these operations on MyISAM tables. See Chapter 4, MySQL Programs.

MySQL programs can be invoked with the --help or -? option to obtain online assistance.

BIT Data Type: Can be used to store numbers in binary notation. See Section 10.1.1, “Overview of Numeric Types”.

Cursors: Elementary support for server-side cursors. For information about using cursors within stored routines, see Section 12.8.5, “Cursors”. For information about using cursors from within the C API, see Section 20.9.7.3, “mysql_stmt_attr_set()”.

Information Schema: The introduction of the INFORMATION_SCHEMA database in MySQL 5.0 provided a standards-compliant means for accessing the MySQL Server's metadata; that is, data about the databases (schemas) on the server and the objects which they contain. See Chapter 19, INFORMATION_SCHEMA Tables.

Instance Manager: Can be used to start and stop the MySQL Server, even from a remote host. See Section 4.6.10, “mysqlmanager — The MySQL Instance Manager”.

Precision Math: MySQL 5.0 introduced stricter criteria for acceptance or rejection of data, and implemented a new library for fixed-point arithmetic. These contributed to a much higher degree of accuracy for mathematical operations and greater control over invalid values. See Section 11.13, “Precision Math”.

Storage Engines: Storage engines added in MySQL 5.0 include ARCHIVE and FEDERATED. See Section 13.8, “The ARCHIVE Storage Engine”, and Section 13.7, “The FEDERATED Storage Engine”.

Stored Routines: Support for named stored procedures and stored functions was implemented in MySQL 5.0. See Section 18.2, “Using Stored Routines (Procedures and Functions)”.

Strict Mode and Standard Error Handling: MySQL 5.0 added a strict mode where by it follows standard SQL in a number of ways in which it did not previously. Support for standard SQLSTATE error messages was also implemented. See Section 5.1.7, “Server SQL Modes”.

Triggers: MySQL 5.0 added limited support for triggers. See Section 18.3, “Using Triggers”, and Section 1.7.5.3, “Stored Routines and Triggers”.

VARCHAR Data Type: The effective maximum length of a VARCHAR column was increased to 65,535 bytes, and stripping of trailing whitespace was eliminated. (The actual maximum length of a VARCHAR is determined by the maximum row size and the character set you use. The maximum effective column length is subject to a row size of 65,535 bytes, which is shared among all columns.) See Section 10.4, “String Types”.

Views: MySQL 5.0 added support for named, updatable views. See Section 18.4, “Using Views”, and Section 1.7.5.5, “Views”.

XA Transactions: See Section 12.4.7, “XA Transactions”.

MySQL Enterprise For assistance in maximizing your usage of the many new features of MySQL, subscribe to MySQL Enterprise. For more information see http://www.mysql.com/products/enterprise/advisors.html.

Performance enhancements: A number of improvements were made in MySQL 5.0 to improve the speed of certain types of queries and in the handling of certain types. These include:

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Migration

MySQL Usage

MySQL Connectors

Programming Languages

Tools

3rd-Party Applications

Storage Engines

MySQL Technology

SQL Standards

Business

#mysql is primarily for MySQL questions, but other database and general SQL questions are welcome. Questions about PHP, Perl, or C in combination with MySQL are also common.

MySQL Enterprise Server

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Organization of data on disk

MySQL Server maps each database to a directory under the MySQL data directory, and maps tables within a database to file names in the database directory. This has a few implications:

Database and table names cannot contain path name separator characters (“/”, “\”).

General language syntax

SQL statement syntax

Data types

Functions and operators

For VARCHAR columns, trailing spaces are removed when the value is stored. (This is fixed in MySQL 5.0.3). See Section B.1.8, “Known Issues in MySQL”.

In some cases, CHAR columns are silently converted to VARCHAR columns when you define a table or alter its structure. (This no longer occurs as of MySQL 5.0.3). See Section 12.1.10.1, “Silent Column Specification Changes”.

There are several differences between the MySQL and standard SQL privilege systems. For example, in MySQL, privileges for a table are not automatically revoked when you delete a table. You must explicitly issue a REVOKE statement to revoke privileges for a table. For more information, see Section 12.5.1.5, “REVOKE Syntax”.

The CAST() function does not support cast to REAL or BIGINT. See Section 11.9, “Cast Functions and Operators”.

Standard SQL requires that a HAVING clause in a SELECT statement be able to refer to columns in the GROUP BY clause. This cannot be done before MySQL 5.0.2.

Michael (Monty) Widenius

David Axmark

Jani Tolonen

Sinisa Milivojevic (now in support)

Tonu Samuel (past developer)

Sasha Pachev (past developer)

Matt Wagner

Miguel Solorzano (now in support)

Timothy Smith (now in development)

Sergei Golubchik

Jeremy Cole (past developer)