The MySQLi Extension (MySQL Improved) is a relational database driver used in the PHP scripting language to provide an interface with MySQL databases.
There are three main API options when considering connecting to a MySQL database server:
- PHP’s MySQL Extension
- PHP’s MySQLi Extension
- PHP Data Objects (PDO)
The PHP code consists of a core, with optional extensions to the core functionality. PHP’s MySQL-related extensions, such as the MySQLi extension, and the MySQL extension, are implemented using the PHP extension framework. An extension typically exposes an API to the PHP developer, to allow its facilities to be used programmatically. However, some extensions which use the PHP extension framework do not expose an API to the PHP developer. Wikipedia