Single Row sub queries

Definition

A single-row subquery is a nested query that returns exactly one row and one column, allowing it to be used with single-row comparison operators like =, >, or <.

Example

SELECT name, salary FROM employees
WHERE salary > (SELECT AVG(salary) FROM employees);

Why Testers Use Them

Single-row subqueries let testers write comparison-based verification queries — for instance, checking that a specific record's value is correctly above or below a computed benchmark like an average.