Specify a test for a non-empty set.


Syntax

<exists predicate> ::= EXISTS <table subquery>


Notes

The predicate evaluates to TRUE if the cardinality of the subquery result is greater than 0, else to FALSE.


Examples

1) The following example selects students enrolled in more than 2 courses:

       SELECT studentID, studentName

       FROM students s

       WHERE EXISTS (

SELECT COUNT( * )

FROM enrolls

WHERE studentID = s.studentID

HAVING COUNT( * ) > 2

       )

2) The following example selects students not enrolled in any courses:

       SELECT studentID, studentName

       FROM students s

       WHERE EXISTS (

SELECT COUNT( * )

FROM enrolls

WHERE studentID = s.studentID

HAVING COUNT( * ) = 0

       )


Conformance

SQL:2003 standard

-

-

Core SQL

Feature T501 "Enhanced EXISTS predicate"

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