Retrieval: Some Advanced Features
This is the fourth chapter in a series about retrieval features of SQL. It is a logical continuation of Chapters 4, 5, and 8.
First, in Section 9.1, we revisit subqueries, beginning with an introduction to the three operators ANY, ALL, and EXISTS. These operators allow you to create a special relationship between main queries and subqueries, as opposed to using the IN operator or standard comparison operators. You will also learn about correlated subqueries, which are subqueries where some subquery clauses refer to column expressions in the main query.
In Sections 9.2 and 9.3, we will look at subqueries ...