SQL: Visual Quickstart Guide, Second Edition

Chapter 8. Subqueries

To this point, I've used a single SELECT statement to retrieve data from one or more tables. This chapter describes nested queries, which let you retrieve or modify data based on another query's result.

A subquery, or subselect, is a SELECT statement embedded in another SQL statement. You can nest a subquery in:

• The SELECT, FROM, WHERE, or HAVING clause of a SELECT statement

• Another subquery

• An INSERT, UPDATE, or DELETE statement

In general, you can use a subquery anywhere an expression is allowed, but your DBMS might restrict where they can appear. This chapter covers subqueries nested in a SELECT statement or another subquery; Chapter 10 covers subqueries embedded in INSERT, UPDATE, and DELETE statements.

Understanding Subqueries ...