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-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 above query can also be written as follows:
SELECT OBJECT(d) FROM DeptBean d WHERE NOT EXISTS d.emps



Related concepts
EJB query language
WHERE clause
Related tasks
Using EJB query
Concept topic Concept topic    

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Last updatedLast updated: Aug 31, 2013 4:28:44 AM CDT
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