Nested Subqueries

Nested Subqueries is a SQL statement in the Subqueries category. Subqueries nested within other subqueries. Can be deeply nested, but may affect readability. The syntax is SELECT * FROM table WHERE column IN (SELECT col FROM (SELECT ...) AS inner_derived);. It returns multi-level filtered result. A typical example: SELECT name, salary FROM employees WHERE dept_id IN ( SELECT id FROM departments WHERE budget > (SELECT AVG(budget) FROM departments) ); -- Employees in departments with above-average budget 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 EXISTS, which returns TRUE if the subquery returns at least one row. Often faster than IN for large datasets.