Preface to the Third Edition If you have had any contact with a relational database, then it is very likely that you have seen the letters "SQL." SQL (Struc- tured Query Language) is a computer language designed to manipulate relational databases. You can use it to define a da- tabase's structure, to modify data, and to retrieve data. This book has been written to give you an in-depth introduc- tion to using SQL, providing a gentle but complete approach to learning the language. You will learn not only SQL syntax, but also how SQL works. Understanding the "how" as well as