SQL EXISTS

The EXISTS operator tests a subquery and returns TRUE if at least one record satisfies it. Otherwise, FALSE is returned.

Syntax

SELECT column1, column2, ...
FROM table_one
WHERE EXISTS (SELECT column1 FROM table_two WHERE condition);

Example

In the example below, the statement returns TRUE for each row in the users table that has a corresponding user_id value in the locked_out table. Otherwise, if there’s no match, the statement returns FALSE.

SELECT *
FROM users
WHERE EXISTS (SELECT user_id FROM locked_out WHERE locked_out.user_id = users.user_id);

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