If you want my advice - which I'm guessing you do, as you posted in a thread 😉 I'd say don't bother buying a book, unless the place that you are coding at doesn't have easy access to the internet.
Purely because all the information you need is on the web. I mean, a short while back, I didn't know anything about php, and now, I got me a working(ish) update script. It's not exactly the most complex and secure thing ever, but I did it.
Plus, with the internet, when you don't understand something that a tutorial says, you can ask some one.
Save your self the cash, unless the book is necessary.