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EXISTS predicate
The exists predicate tests for the presence or absence of a condition specified by a subselect.
Use the syntax:
EXISTS ( subselect )EXISTS collection-valued-path-expressionThe 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 above query can also be written as follows:
SELECT OBJECT(d) FROM DeptBean d WHERE NOT EXISTS d.emps
EJB query language
WHERE clause
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