Network Deployment (Distributed operating systems), v8.0 > Develop and deploying applications > Develop Dynamic and EJB query > Develop applications that use EJB query > EJB query language > WHERE clause
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
EJB query language
Use EJB query