The EXISTS
predicate checks whether a result table (see result table name) contains at least one row.Syntax
<exists_predicate> ::= EXISTS <subquery>
subqueryExplanation
The truth content of an EXISTS predicate is either true or false.
The subquery generates a result table. If this result table contains at least one row,
EXISTS <subquery> is true.Model table
Only select customers that have one or more reservations:
SELECT * FROM customer WHERE EXISTS
(SELECT * FROM reservation WHERE customer.cno = reservation.cno)