SQL · Pattern 8 — Subqueries
EXISTS
The EXISTS operator returns TRUE if the subquery returns at least one row.
Source data — Pattern 8: Subqueries
All queries run against the shared employees and departments tables (see schema.sql). This pattern introduces scalar, correlated, and multiple-row subqueries. Topics 47 and 48 demonstrate the EXISTS and NOT EXISTS operators, while Topics 49 and 50 introduce the ANY (SOME) and ALL comparison operators.
What it does
The EXISTS operator returns TRUE if the subquery returns at least one row.
Problem
Find departments that have employees.
SELECT department_name
FROM departments d
WHERE EXISTS (
SELECT 1
FROM employees e
WHERE e.department_id = d.department_id
);
Result
