A four part tutorial that explains the PHP / MySQL extensions - mysql, mysqli, and pdo_mysql - with simple examples is now accessible from Sun Developer Network. While most of the information presented in the tutorial is available elsewhere in bits and pieces, the real value-add is in the introduction of the MySQL native driver for PHP, mysqlnd.
Here is a brief description of all four parts in the series. Check them out, and as always feel free to send the corrections, comments, suggestions, etc., to my Sun mail ID: Giri.Mandalika@Sun.COM
Part 1: Using the MySQL Improved Extension, mysqli -- describes mysqli, the MySQL Improved Extension that is the successor to the mysql extension