EXISTS predicate

The exists predicate tests for the presence or absence of a condition specified by a subselect.

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

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EJB query language
WHERE clause

Using EJB query
    

 

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