Writing SQL statements requires a good understanding of the underlying database design. Without knowing what information is stored in what table, how tables are related to each other, and the actual breakup of data within a row, it is impossible to write effective SQL.
You are strongly advised to actually try every example in every lesson in this book. All the lessons use a common set of data files. To assist you in better understanding the examples, and to enable you to follow along with the lessons, this appendix describes the tables used, their relationships, and how to build (or obtain) them.