This chapter discusses a selection of fairly independent SQL features that are of importance for the tuning process, many of which are somewhat poorly advertised. I’ll begin with a quick review of just what SQL statements are and the identifiers used to refer to them. My second topic is the array interface that is used to move data from client processes to the database server in large batches. I will then discuss factored subqueries that make reading SQL statements much easier. My fourth and final topic in this first chapter is a review of the different types of inner and outer joins; I will explain how to write them, what they are used for, and why it isn’t quite as easy to reorder outer joins as it is to reorder inner joins.