EXISTS

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.

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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