EXISTS Predicate

A predicate that is true when its subquery returns at least one row.

What does EXISTS Predicate do in a relational database?

EXISTS Predicate — A predicate that is true when its subquery returns at least one row.

SELECT customer_id
FROM customer
WHERE EXISTS (
    SELECT 1
    FROM purchase_order
    WHERE purchase_order.customer_id = customer.customer_id
);

Level: Apprentice · More Database terms at this level

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