A very nice introduction to the background of SQL. That behind it sits a database that can be constructed via a systematic set of rules that can be applied to data. All the standard normal forms are discussed, as one might expect.
You don't need to know the predicate calculus for this book. The mathematical treatment should not be difficult to those who have already had university level courses on computer science.
The book is not geared towards any vendor's implementation of SQL. Which is good. You can apply this book towards any of the major vendors' offerings.
