Located at http://www.sitepoint.com/books/, the Website supporting this book will give you access to the following facilities:
As you progress through the text, you'll note a number of references to the code archive. This is a downloadable ZIP archive that contains complete code for all the examples presented in the book.
No book is perfect, and even though this is a second edition, I expect that watchful readers will be able to spot at least one or two mistakes before the end of this one. Also, PHP and MySQL (and even the Web in general) are moving targets, constantly undergoing changes with each new release. The Errata page on the book's Website will always have the latest information about known typographical and code errors, and necessary updates for changes to PHP and MySQL.