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EXISTS Predicate (exists_predicate) 

The EXISTS predicate ( exists_predicate) checks whether a result table (see result table name) contains at least one row.

Syntax

<exists_predicate> ::= EXISTS <subquery>

subquery

Explanation

The truth content of an EXISTS predicate is either true or false.

The subquery generates a result table. If this result table contains at least one row, EXISTS <subquery> is true.

Example tables: customer, reservation

Only select customers that have one or more reservations:

SELECT * FROM customer WHERE EXISTS
(SELECT * FROM reservation WHERE customer.cno = reservation.cno)

CNO

TITLE

NAME

FIRSTNAME

ZIP

CITY

ACCOUNT

3000

Mrs

Porter

Jenny

80335

New York

100.00

3100

Comp

DATASOFT

?

50933

Dallas

4813.50

3200

Mr

Porter

Martin

10969

Los Angeles

0.00

3600

Mr

Howe

George

81737

New York

-315.40

3900

Mrs

Brown

Susan

13599

Los Angeles

-4167.79

4100

Mr

Adams

Thomas

13355

Los Angeles

-416.88

4300

Comp

TOOLware

?

13629

Los Angeles

3770.50

4400

Mrs

Brown

Rose

40233

Hollywood

440.00

 

 

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