I just read this excelent article from the IBM's developerWorks website, it's name is Five common PHP database problems.

This article shows five database problems that occur in PHP applications as well as their solutions and include database schema design, database access, and the business logic code that uses the database.

It is a bit older -a year ago more or less- but i think that can be helpful for everybody that works with PHP and MySql.

Best regards,