Disable/Enable a Constraint on a table

ALTER TABLE TableName <CHECK / NOCHECK> CONSTRAINT ConstraintName

GO

Examples:

--disable constraint 

ALTER TABLE dbo.StamTable2 NOCHECK CONSTRAINT StamTable2_check

GO

--enable constraint 

ALTER TABLE dbo.StamTable2 CHECK CONSTRAINT StamTable2_check

GO 

--disable all constraints for the dbo.StamTable2 table 

ALTER TABLE dbo.StamTable2 NOCHECK CONSTRAINT ALL  

GO

--enable all constraints for the dbo.StamTable2 table 

ALTER TABLE dbo.StamTable2 CHECK CONSTRAINT ALL  

GO

NOTE: This action applies only to foreign key and check constraints.