The back of this book claims that "This is the SQL reference you'll reach for first!" and I can personally support their claim. It is easily the best organized SQL reference that I have encountered. It contains alphabetical listings of all SQL data types and their related functions, in-depth instruction on data definition (create, alter, drop, etc.) and comprehensive descriptions and examples of all data manipulation methods (insert, update, delete, etc.).
The only possible drawback of this book is that it is not, nor is it intended to be, an instruction manual for SQL. The book cuts right to the point, and only tells you exactly what you need to know. For beginners, this book would not be a good starting point, but for people with at least some exposure to SQL, this book will probably never leave your desk.