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This check constraint has the following definition Provides a place for you to type the check constraint. A column check constraint is used to ensure that no inappropriate values are entered into any column of the specified type, while a table check constraint ensures that no row in a table violates the constraint.
You can enforce a particular formatting requirement. For example, if a table has a column for phone numbers you may want to ensure that users enter them all in the same manner. For North American phone numbers, you could use a constraint such as:
CHECK ( Phone LIKE '(___) ___-____' );
Once this CHECK condition is in place, if you attempt to set a Phone value to 9835, for example, the change is not allowed.
For example, you can add a constraint on the Employees table to ensure that the TerminationDate is always later than, or equal to, the StartDate:
CHECK(TerminationDate >= StartDate);
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