First I got started with the mysql through the online documentation avilable at mysql's website, which is written and being maintained by Paul Dubois.
After that I decided to buy the book, and I was very satisfied with my decision. Below I am listing several evaluative criterias that indeed make the book ( and the author, as well) the best choice available thus far:
1) Great for beginners: To understand how to keep a grade book, you don't need huge brains(I hope so). That's exactly what Paul starts his book with, and makes his way through to some RDBMS terminologies that you won't even notice.
2) From the simplest to more advanced... Such books make the learning for beginniners piece of cake, and for experienced ones a lof of fun. The book's focus is on couple of tables that you build in the first chapter, and keep manipulating throughout the book. Paul never forgets about those tables. Even in the Second section of the book (Using MySQL Programming Interfaces), he teaches you to write applications using C, Perl and PHP to manipulate them. Since you build them all together with Paul, you have more understanding of what you're doing. Of course, by the end of the book it gets advanced, which makes it the right choise for advanced programmers as well.
3) Great references Oh yes. Awesome appendixes. Listings of all the functions, keywords, syntaxes are available (in alphabetical order). Also seperate appendixes for Perl DBI API, C API and PHP API makes it even more useful
4) Easy language. This is deginitely important. Even though the books are in english, not all of them gurantee you comprehension. Sometimes you might find the lingo of the book of too high a level, or even vice versa. None of those are the cases with the MySQL book. Paul uses plain english and switches to RDBMS lingo whenever he thinks it is appropriate.
5) The book is definitely from an expert. You better don't doubt it! Since Paul is the one in charge of the official documentation, who else could tell you more about the subject?
6) Still got the gap? Let him fill it... Another thing that pleased was the fact, unlike other aUtHoRs, it is not hard to get hold of Paul in mysql mailing list. He is kind enough to answer the questions, and/or contribute to the discussions about the subject.
If you are interested with learning MySql, I want you to buy the book, because there're no other books better than this one so far. Also, support for such authors is important.