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Editorial Team
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Asked: 2026-05-18T03:45:15+00:00

When I right click on a default constraint and I ask SQL Server to

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When I right click on a default constraint and I ask SQL Server to create a CREATE script for it, it generates the following code: 

ALTER TABLE [dbo].[tblEventTurnJudgeStartValues]  WITH NOCHECK ADD  CONSTRAINT [tblEventTurnJudgeStartValues_ExecutionToggle] CHECK  (([ExecutionToggle]=(1) OR [ExecutionToggle]=(0) OR [ExecutionToggle]=(-1)))
GO
ALTER TABLE [dbo].[tblEventTurnJudgeStartValues] CHECK CONSTRAINT [tblEventTurnJudgeStartValues_ExecutionToggle]

For the record, I understand the first ALTER statement but I do not understand what the the second alter statement does. Tried to google the “CHECK CONSTRAINT” phrase but only got hits on the add constraint syntax.

Thanks.

Seth

update
Thanks Joe for your answer. Found this link which helps.

http://blog.sqlauthority.com/2009/11/12/sql-server-disable-check-constraint-enable-check-constraint/

I did not know that you could enable and disable constraints. Cool!

Seth

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1 Answer

  1. Editorial Team

    The first statement creates the constraint, but since it is created with NOCHECK, existing data is not validated at the time of creation.

    The second statement simply turns the constraint on and is technically redundant.

    Personally, I’d prefer the second statement be written with the WITH CHECK option, which will validate all existing data against the constraint and will prevent the constraint from becoming untrusted.

    ALTER TABLE [dbo].[tblEventTurnJudgeStartValues] WITH CHECK CHECK CONSTRAINT [tblEventTurnJudgeStartValues_ExecutionToggle]
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