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 Windows Systems
MySQLi is not enabled by default, so the
php_mysqli.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_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
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.