Although the data type of a column restricts the values that are allowed in that column (for example, only numbers or only dates), you may want to further restrict the allowed values.
You can restrict the values of any column by specifying a CHECK constraint. You can use any valid condition that could appear in a WHERE clause to restrict the allowed values. Most CHECK constraints use either the BETWEEN or IN condition.
For more information about valid conditions, see Search conditions. For more information about assigning constraints to tables and columns, see Ensuring Data Integrity.