Adding a CHECK Constraint to an Existing Table : Check « Constraints « SQL Server / T-SQL Tutorial

You can add a CHECK constraint to an existing table using ALTER TABLE and ADD CONSTRAINT.

The syntax is as follows:

ALTER TABLE table_name
WITH CHECK | WITH NOCHECK
ADD CONSTRAINT  constraint_name
CHECK ( logical_expression )


CHECK           With the CHECK option (the default), existing data is validated against the new CHECK constraint.
WITH NOCHECK    NOCHECK skips validation of new data, limiting the constraint to validation of new values (inserted or updated).

7.5.Check
	7.5.1.	Using CHECK Constraints
	7.5.2.	Adding a CHECK Constraint to an Existing Table
	7.5.3.	Constraints with name
	7.5.4.	CHECK Clause
	7.5.5.	Check Constraint
	7.5.6.	CHECK (DATEPART(DAY, GETDATE()) < 28)
	7.5.7.	A check constraint uses an expression to qualify records that are acceptable for any Inserts or Updates
	7.5.8.	Use or to link two conditions for check constraint
	7.5.9.	Using a Multicolumn CHECK Constraint
	7.5.10.	Check for data length
	7.5.11.	Pattern based constraint
	7.5.12.	Mark nocheck for a constraint
	7.5.13.	A table-level check constraint that limits Banker IDs to a specific format