PHP MySQL developers are confronted with three PHP MySQL APIs. That is confusing. Since mid 2012 the PHP manual suggests not to use the oldest and original PHP MySQL extension any more to cure the situation. Please, swap out ext/mysql in favour of either ext/mysqli or PDO_MySQL. Why to upgrade is below. Read on, if you are a PHP beginner, your PHP application is still using mysql_* functions of ext/mysql or you are a PHP trainer.
As a PHP consumer, tease your software vendors by asking whether they use the state of the art APIs! Here is a cut&paste test question to ask your vendor: do you support secure SSL connections to MySQL?