Check Constrain Based on Another Column

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Check Constrain Based on Another Column

Author

Topic

user79
Starting Member

2 Posts

Posted - 2012-05-04 : 00:25:49

Hi i have Table A - Column A,Column B

Column B can not be a null value if Coulmn A = "xxx", how can i do this.

Thanks.

user79
Starting Member

2 Posts

Posted - 2012-05-04 : 03:10:06

alter table Contacts
add constraint chkRegion CHECK ((REGION IS NOT NULL AND Country = 'USA') OR (REGION IS NULL AND Country <> 'USA') OR (REGION IS NOT NULL AND Country <> 'USA'))

Lamprey
Master Smack Fu Yak Hacker

4614 Posts

Posted - 2012-05-04 : 13:47:09

Hu?

REGION IS NOT NULL AND Country = 'USA' 
REGION IS NOT NULL AND Country <> 'USA'

RL
Starting Member

15 Posts

Posted - 2012-05-04 : 15:56:18

Cleaner way to express the same logic:

alter table Contacts
add constraint chkRegion CHECK (country <> 'USA' OR region IS NOT NULL);

INSERT INTO Contacts SELECT 'USA', NULL; -- FAILS
INSERT INTO Contacts SELECT 'USA', 'East' -- OK;
INSERT INTO Contacts SELECT 'CAN', NULL; -- OK
INSERT INTO Contacts SELECT NULL, NULL; -- OK

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