Exists Predicate
Wed, 03/04/2009 - 20:02 | 
hdanzl
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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