Mysqli not installed?

I get the following error: Fatal error: Class ‘mysqli’ not found in my php script I have php5.3.3-7 installed and I get this when I run apt-cache show php5-mysql

Description: MySQL module for php5
 This package provides modules for MySQL database connections directly from
 PHP scripts.  It includes the generic "mysql" module which can be used
 to connect to all versions of MySQL, an improved "mysqli" module for
 MySQL version 4.1 or later, and the pdo_mysql module for use with
 the PHP Data Object extension.

There is nothing about mysql at all in php info. How do I find the extention and do I have to istall it? There are many references to mysqli in my php.ini. But something is wrong.

Answer

Have you actually installed the php5-mysql package? apt-cache show will give you information on packages that aren’t installed (you want dpkg -l to list installed packages). If the package is installed, double-check that it’s enabled (/etc/php5/conf.d/mysql.ini is the place to look).