For compiling, simply use the --with-mysql[=DIR] configuration option where the optional [DIR] points to the MySQL installation directory.
Although this MySQL extension is compatible with MySQL 4.1.0 and greater, it doesn't support the extra functionality that these versions provide. For that, use the MySQLi extension.
If you would like to install the mysql extension along with the mysqli extension you have to use the same client library to avoid any conflicts.
Installation on Linux Systems
The option --with-mysql is enabled by default. This default behavior may be disabled with the --without-mysql configure option. If MySQL is enabled without specifying the path to the MySQL install DIR, PHP will use the bundled MySQL client libraries.
Users who run other applications that use MySQL (for example, auth-mysql) should not use the bundled library, but rather specify the path to MySQL's install directory, like so: --with-mysql=/path/to/mysql . This will force PHP to use the client libraries installed by MySQL, thus avoiding any conflicts.
PHP 5.0.x, 5.1.x, 5.2.x
MySQL is not enabled by default, nor is the MySQL library bundled with PHP. Read this FAQ for details on why. Use the --with-mysql[=DIR] configure option to include MySQL support. You can download headers and libraries from » MySQL.
In PHP 5.3.0 and above the MySQL-related database extensions use the MySQL Native Driver by default. This means that the MySQL Client Library (libmysql) is no longer required in order to support connection to a MySQL database. The extensions mysql, mysqli, and PHP_PDO_MYSQL are all enabled by default in PHP 5.3.0+, and all use the MySQL Native Driver by default. In each case no further installation steps are required in order to use these extensions, although you may want to set some preferences in php.ini depending on your requirements.
Installation on Windows Systems
The PHP MySQL extension is compiled into PHP.
PHP 5.0.x, 5.1.x, 5.2.x
MySQL is no longer enabled by default, so the php_mysql.dll DLL must be enabled inside of php.ini. Also, PHP needs access to the MySQL client library. A file named libmysql.dll is included in the Windows PHP distribution and in order for PHP to talk to MySQL this file needs to be available to the Windows systems PATH. See the FAQ titled "How do I add my PHP directory to the PATH on Windows" for information on how to do this. Although copying libmysql.dll to the Windows system directory also works (because the system directory is by default in the system's PATH), it's not recommended.
As with enabling any PHP extension (such as php_mysql.dll), the PHP directive extension_dir should be set to the directory where the PHP extensions are located. See also the Manual Windows Installation Instructions. An example extension_dir value for PHP 5 is c:\php\ext
If when starting the web server an error similar to the following occurs: "Unable to load dynamic library './php_mysql.dll'", this is because php_mysql.dll and/or libmysql.dll cannot be found by the system.
Please refer to these notes on installing MySQL support on PHP 5.3.0 and above.
MySQL Installation Notes
Crashes and startup problems of PHP may be encountered when loading this extension in conjunction with the recode extension. See the recode extension for more information.
If you need charsets other than latin (default), you have to install external (not bundled) libmysql with compiled charset support.