Subqueries and Set Operators: Correlated Subqueries, EXISTS, the NOT IN Trap and UNION/INTERSECT/EXCEPT
A subquery uses one query's result inside another; NOT IN returns no rows at all if the list holds a single NULL. We cover scalar subqueries and error 512, IN/ANY/ALL, correlated subqueries, derived tables, EXISTS versus NOT EXISTS, and UNION, UNION ALL, INTERSECT and EXCEPT on Bookstore data with real output, logical reads and plan comparisons.
8 Nov 2026
·
14 min
·
4
