Hi,

I need to enforce that a table does not have "duplicates" for a
specific status type in the table.

If the column "STATUS" = 2, then there can not be more than one row
with a specific "ID" column.

I can not use a unique key constraint because duplicate values for this
combo of columns is valid for the status = 1.

Just when the status = 2, there can not be any other rows with the same
ID and status = 2.

Any ideas?

-Paul

Please post DDL, so that people do not have to guess what the keys,
constraints, Declarative Referential Integrity, datatypes, etc. in your
schema are. Sample data is also a good idea, along with clear
specifications.

CHECK constraint work at row-by-row basis. I suggest you use a trigger instead.

--
Tibor Karaszi, SQL Server MVP
http://www.karaszi.com/sqlserver/default.asp
http://www.solidqualitylearning.com/
http://www.sqlug.se/


[quoted text, click to view]

[quoted text, click to view]

Hi Paul,

Apart from the trigger Tibor suggests, there are two other options:

1. Use an indexed view:

CREATE VIEW Status2Only
WITH SCHEMABINDING
AS
SELECT SpecificID -- You may add other columns,
-- if that helps for other purposes
FROM dbo.MyTable
WHERE Status = 2
go
CREATE UNIQUE CLUSTERED INDEX NoDupsFor2 ON Status2Only(SpecificID)
go

2. Use a computed column (assuming PKCol is the primary key):

ALTER TABLE MyTable
ADD HelperColumn AS CASE
WHEN Status = 2
THEN SpecificID
ELSE PKCol
END
go
ALTER TABLE MyTable
ADD CONSTRAINT NoDupsFor2 UNIQUE (Status, HelperColumn)
go

(both versions untested - bewarer of typos!)

Best, Hugo
--