The best book that helped me, without a doubt, was SQL: A Beginner's Guide. This had to be one of the most boring books I've read (very very plain) but I learned so much from it. Very, very useful book, I would not have learned SQL with out it. Bonus is that it teaches you SQL, not MySQL, not T-SQL, not PostgreSQL, not SQL Server: just plain SQL. It does highlight nuances where necessary, but otherwise it's just SQL.
Coincidentally, the second book I read was Beginning MySQL, which was by the same author, Robert Sheldon (I didn't realize it until just now, lol). Again, a very helpful book. I really like Wrox Publishing, they do good books. I would also recommend any book by O'Reilly publishing or Apress as well (can't go wrong with either).
Once you get a handle on the SQL language itself, then you should (need) to read MySQL 5.0 Certification Study Guide, especially if you plan on being a DBA. You'll want to get your CMDBA and this book will help. I just found out the other day at work that there aren't near as many CMDBA's in the country as I thought (I think I heard them say under 1000). We're a rare breed (yes I have my CMDBA), and they pay us well ;)
Lastly, after you have your CMDBA, read High Performance MySQL, the 2nd edition by Baron Schwartz, Peter Zaitsev, Vadim Tkachenko, Jeremy Zawodny, Arjen Lentz, and Derek J. Balling. Zaitsev, Tkachenko, and Schwartz work for Percona (CEO/Founder, CTO/Co-Founder, and VP of Consulting respectively). Percona pretty much has the most brilliant minds in the world when it comes to MySQL, and that's not an overstatement. We've worked with some of them before and words can describe their brilliance.
I hope this helps to maybe give some direction. Good Luck.