Subquery with UNION inside
Subquery with UNION inside is a SQL statement in the Subqueries category. A derived table containing a UNION operation inside, filtered by the outer query. The syntax is SELECT * FROM (SELECT ... UNION ALL SELECT ...) AS combined WHERE condition;. It returns unioned subquery result. A typical example: SELECT name, total FROM ( SELECT customer_name AS name, SUM(amount) AS total FROM orders GROUP BY customer_name UNION ALL SELECT department AS name, SUM(salary) AS total FROM employees GROUP BY department ) AS combined WHERE total > 10000 ORDER BY total DESC; -- Combines customer orders and employee salaries into one report -- Filters only large totals -- Useful for comparing metrics across different entities 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.