WITH CHECK ADD CONSTRAINT followed by CHECK CONSTRAINT vs. ADD CONSTRAINT

Question

I\'m looking at the AdventureWorks sample database for SQL Server 2008, and I see in their creation scripts that they tend to use the following:

ALTER TABLE          


        

Answer 1

Further to the above excellent comments about trusted constraints:

select * from sys.foreign_keys where is_not_trusted = 1 ;
select * from sys.check_constraints where is_not_trusted = 1 ;

An untrusted constraint, much as its name suggests, cannot be trusted to accurately represent the state of the data in the table right now. It can, however, but can be trusted to check data added and modified in the future.

Additionally, untrusted constraints are disregarded by the query optimiser.

The code to enable check constraints and foreign key constraints is pretty bad, with three meanings of the word "check".

ALTER TABLE [Production].[ProductCostHistory] 
WITH CHECK -- This means "Check the existing data in the table".
CHECK CONSTRAINT -- This means "enable the check or foreign key constraint".
[FK_ProductCostHistory_Product_ProductID] -- The name of the check or foreign key constraint, or "ALL".