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Exists Predicate

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NexusDB V3 Manual

Exists Predicate

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NexusDB Manual V3 > SQL Reference > Predicates

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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