Subquery in SELECT
Subquery in SELECT is a SQL statement in the Subqueries category. A scalar subquery in the SELECT clause that computes a value for each row. The syntax is SELECT column1, (SELECT aggregate FROM table2) AS alias FROM table1;. It returns computed column per row. A typical example: SELECT name, salary, (SELECT MAX(salary) FROM employees) AS max_salary, ((salary * 100.0) / (SELECT MAX(salary) FROM employees)) AS pct_of_max FROM employees; -- Each row shows salary as percentage of the maximum 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.