Marko Heijnen

CodeKitchen

MySQL_* functions is deprecated and this plugin creates a layer to use MySQLi instead. So you don’t get notices when using PHP 5.5
Be sure to read the installation instructions, as this is not a traditional plugin, and on activation you do need to install our database driver by using the settings screen or move manually db.php into your content directory.

MySQLi database layer

I was restoring an old WordPress site (v3.7.1) that I haven't touched in over 3 years that on my WAMP server. Even though this plugin hasn't been updated for just as long, it was helpful in fixing the depreciation notices that I was getting for mysqli, thank you.



Helpful when running dated WordPress sites

MySQL_* functions are deprecated and this plugin creates a layer to use MySQLi instead. So you don't get notices when using PHP 5.5

Kurt Payne

This plugin adds an improved database layer to WordPress. It allows you to do more then the default one and is always up-to-date with the changes core makes.
mysql_* functions
The mysql_* functions are officially deprecated for PHP 5.5 and are throwing E_DEPRECATED errors. 
On https://core.trac.wordpress.org/ticket/21663 there is discussion on this topic.
This plugin reflects those discussions.
Why should I use this plugin?
You should use this plugin if you want to start using PDO / MySQLi for WordPress.

MySQLi database layer vs WP DB Driver