EXISTS

EXISTS is a SQL statement in the Subqueries category. Returns TRUE if the subquery returns at least one row. Often faster than IN for large datasets. The syntax is SELECT * FROM table1 WHERE EXISTS (SELECT 1 FROM table2 WHERE condition);. It returns boolean (exist check). A typical example: SELECT d.name FROM departments d WHERE EXISTS (SELECT 1 FROM employees e WHERE e.dept_id = d.id); -- Departments that have at least one employee A close relative is Scalar Subquery, which a subquery that returns a single value (one row, one column). Can be used in SELECT, WHERE, HAVING clauses. A close relative is Correlated Subquery, which a subquery that references columns from the outer query. Evaluated for each row of the outer query. A close relative is IN Subquery, which checks if a value matches any value returned by the subquery. More about this category: Nested queries — correlated, EXISTS, IN, ANY, ALL, scalar subqueries.