That said, because PHP is primarily a Web technology, it will help if you have at least some knowledge of other Web technologies, particularly HTML and CSS.

Many Web applications make use of a database to store data, and this book contains three chapters on working with MySQL databases. Once again, if you're already familiar with databases in general -- and MySQL in particular -- you'll be able to fly through these chapters. However, even if you've never touched a database before in your life, you should still be able to pick up a working knowledge by reading through these chapters.