EXISTS

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Remarks

Use the EXISTS keyword to test whether rows exist in the result of the subquery. For every row the outer query evaluates, Pervasive.SQL V8 tests for the existence of a related row from the subquery. Pervasive.SQL V8 includes in the statement's result table each row from the outer query that corresponds to a related row from the subquery.

In most cases, a subquery with EXISTS can be rewritten to use IN. The SRDE can process the query more efficiently if the query uses IN.

Examples

The following statement returns a list containing only persons who have a 4.0 grade point average:

SELECT * FROM Person p WHERE EXISTS 
(SELECT * FROM Enrolls e WHERE e.Student_ID = p.id 
AND Grade = 4.0) 

This statement can be rewritten to use IN:

SELECT * FROM Person p WHERE p.id IN 
(SELECT e.Student_ID FROM Enrolls WHERE Grade = 4.0) 

See Also

SELECT