Subqueries

A subquery is a SELECT statement embedded within another SELECT statement. The embedded subquery is often referenced as the query's inner statement, while the containing query is typically referenced as the query's statement, or outer query block. A subquery returns data that the outer query uses as a condition to determine what data to retrieve. There is no limit to the number of nested subqueries you can create.

Like any query, a subquery returns records from a table that might consist of a single column and record, a single column with multiple records, or multiple columns and records. Subqueries can be noncorrelated or correlated. You can also use them to update or delete table records, based on values in other database tables.