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Asked: 2026-05-11T02:54:24+00:00

How do I create a unique constraint on a varchar field that is case

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How do I create a unique constraint on a varchar field that is case sensitive (SQL Server 2005)?

Currently my constraint looks like this:

alter table MyTable add constraint UK_MyTable_MyUniqueKey unique nonclustered (MyCol)

When I try to insert the following two values, I get a ‘Violation of UNIQUE KEY constraint…’ error.

insert into MyTable (MyCol) values ('ABC') insert into MyTable (MyCol) values ('abc') --causes a violation of UNIQUE KEY constraint 'UK_MyTable_MyUnqiueKey'

I would like the two differently-cased values to be handled as unqiue. I imagine it will involve the following code, but I do not know how it changes my add constraint syntax.

COLLATE SQL_Latin1_General_CP1_CS_AS
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1 Answer

  1. This will change the column to be case sensitive. I don’t think there’s any change to your constraint…

    ALTER TABLE mytable  ALTER COLUMN mycolumn VARCHAR(10)  COLLATE SQL_Latin1_General_CP1_CS_AS

    Any selects or joins on this column will become case sensitive as a result of this operation.

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