The mysqli extension was introduced with PHP version 5.0.0. The MySQL Native Driver was included in PHP version 5.3.0.
Installation on Linux
The common Unix distributions include binary versions of PHP that can be installed. Although these binary versions are typically built with support for MySQL extensions enabled, the extension libraries themselves may need to be installed using an additional package. Check the package manager than comes with your chosen distribution for availability.
Unless your Unix distribution comes with a binary package of PHP with the mysqli extension available, you will need to build PHP from source code. Building PHP from source allows you to specify the MySQL extensions you want to use, as well as your choice of client library for each extension.
PHP 5.0, 5.1, 5.2
If building from source code, to ensure that the mysqli extension for PHP is enabled, you will need to configure the PHP source code to use mysqli. This is achieved by running the configure script with the option --with-mysqli=mysql_config_path/mysql_config , prior to building PHP. This will enable mysqli and it will use the MySQL Client Library (libmysql) to communicate with the MySQL Server.
The mysql_config_path represents the location of the mysql_config program that comes with MySQL Server.
With versions of PHP 5.3.0 and newer, mysqli uses MySQL Native Driver by default. This gives a number of benefits over libmysql.
This is the recommended option, as using the MySQL Native Driver results in improved performance and gives access to features not available when using the MySQL Client Library. Refer to What is PHP's MySQL Native Driver? for a brief overview of the advantages of MySQL Native Driver.
To use MySQL Native Driver with mysqli you need to configure the PHP source code using the --with-mysqli=mysqlnd option, prior to building PHP.
Note that it is possible to freely mix MySQL extensions and client libraries. For example, it is possible to enable the MySQL extension to use the MySQL Client Library (libmysql), while configuring the mysqli extension to use the MySQL Native Driver. However, all permutations of extension and client library are possible.
The following example builds the MySQL extension to use the MySQL Client Library, and the mysqli and PDO MYSQL extensions to use the MySQL Native Driver:
./configure --with-mysql=/usr/bin/mysql_config \ --with-mysqli=mysqlnd \ --with-pdo-mysql=mysqlnd [other options]
Installation on Windows Systems
On Windows, PHP is most commonly installed using the binary installer.
PHP 5.0, 5.1, 5.2
Once PHP has been installed, some configuration is required to enable mysqli and specify the client library you want it to use.
The mysqli extension is not enabled by default, so the php_mysqli.dll DLL must be enabled inside of php.ini. In order to do this you need to find the php.ini file (typically located in c:\php), and make sure you remove the comment (semi-colon) from the start of the line extension=php_mysqli.dll, in the section marked [PHP_MYSQLI].
Also, if you want to use the MySQL Client Library with mysqli, you need to make sure PHP can access the client library file. The MySQL Client Library is included as a file named libmysql.dll in the Windows PHP distribution. This file needs to be available in the Windows system's PATH environment variable, so that it can be successfully loaded. See the FAQ titled "How do I add my PHP directory to the PATH on Windows" for information on how to do this. Copying libmysql.dll to the Windows system directory (typically c:\Windows\system) also works, as the system directory is by default in the system's PATH. However, this practice is strongly discouraged.
As with enabling any PHP extension (such as php_mysqli.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_mysqli.dll'", this is because php_mysqli.dll and/or libmysql.dll cannot be found by the system.
On Windows, for PHP versions 5.3 and newer, the mysqli extension is enabled and uses the MySQL Native Driver by default. This means you don't need to worry about configuring access to libmysql.dll.