PostgreSQL Development Essentials

Subqueries that return multiple rows

In the previous section, we saw subqueries that only returned a single result because an aggregate function was used in the subquery. Subqueries can also return zero or more rows.

Subqueries that return multiple rows can be used with the ALL, IN, ANY, or SOME operators. We can also negate the condition like NOT IN.

Correlated subqueries

A subquery that references one or more columns from its containing SQL statement is called a correlated subquery. Unlike non-correlated subqueries that are executed exactly once prior to the execution of a containing statement, a correlated subquery is executed once for each candidate row in the intermediate result set of the containing query.

The following statement illustrates ...