SQL supports the EXISTS (∃) logical quantifier for testing the result of subquery search conditions. See Specifying Subqueries in Search Conditions. For more information about the EXISTS quantifier, see Teradata Vantage™ SQL Functions, Expressions, and Predicates, B035-1145.
If the subquery would return response rows, then the WHERE condition is considered to be satisfied. Specifying the NOT qualifier for the EXISTS predicate inverts the test.
A subquery used in a search condition does not return any rows. It returns a boolean value to indicate whether responses would or would not be returned.
The subquery can be correlated with an outer query.