I didn't think much of this book, I'm sorry to say.
I found the organization of the book haphazard and poorly thought out. Also, the database schemas used in this book were somewhat confusing, even for an advanced user of the Oracle database and SQLJ like me. The book does a poor job explaining the simple aspects of SQLJ, but also doesn't cover the advanced aspects of the language well either.
This book suffers from having too many authors, none of whom really seem to understand the details of SQLJ very well, or at least, they don't do a good job explaining them to the reader!
I like SQLJ, and there's no doubt that SQLJ is a more efficient way to access a database from Java than using JDBC, but I wouldn't want to learn SQLJ from this book.
I hate to say this, save your money: buy a different book on SQLJ