Retrieval: Multiple Tables and Aggregation
Section 8.1 introduces the concept of row or tuple variables. We did not discuss them so far, because we haven’t needed them up to now. By the way, most SQL textbooks don’t mention tuple variables at all—at least not the way this book does. When you start specifying multiple tables in the FROM clause of your SELECT statements, it is a good idea to start using tuple variables (also referred to as table aliases in Oracle) in a consistent way.
Section 8.2 explains ...