Answer
EXISTS is true when its subquery returns at least one row. • The selected expressions inside the subquery do not determine the Boolean result. • It is commonly used for correlated existence tests. • NOT EXISTS tests that no matching row exists.
💡 SQL Example
SELECT name FROM departments d WHERE EXISTS (SELECT 1 FROM employees e WHERE e.department_id = d.department_id);
Result
Departments with employees
⚡ Quick Revision
EXISTS checks whether a subquery produces any row.