SQL · Functions and expressions

exists

Tests whether a subquery returns any row. Often clearer and faster than IN with nulls.

sqlRunnable example sql course

Syntax

where exists (select 1 …)

Example

Open in the lab

WITH lessons(course_id) AS (VALUES (1))
SELECT 'has lessons' AS result WHERE EXISTS (SELECT 1 FROM lessons WHERE course_id = 1);

Reference pages are the quick answer. The course explains the why, shows the full example and ends with a challenge.