EXISTS predicate
The exists predicate tests for the presence or absence of a condition specified by a subselect.
Use the following
syntax:
EXISTS ( subselect )
EXISTS collection-valued-path-expression
The result of EXISTS is true if the subselect returns at least one value or the path expression evaluates to a nonempty collection, otherwise the result is false.
To negate an EXISTS predicate, precede it with the logical operator NOT.
Example: EXISTS predicate
Return departments that have at least one employee earning more than
1000000:
SELECT OBJECT(d) FROM DeptBean d
WHERE EXISTS ( SELECT 1 FROM IN (d.emps) e WHERE e.salary > 1000000 )
Return departments that have no
employees:
SELECT OBJECT(d) FROM DeptBean d
WHERE NOT EXISTS ( SELECT 1 FROM IN (d.emps) e)
The previous query can also be written as
follows:
SELECT OBJECT(d) FROM DeptBean d WHERE NOT EXISTS d.emps