There are two ways to modify a CHECK condition defined on a table.
Add a new CHECK condition using ALTER TABLE with an ADD table-constraint clause.
Delete all existing CHECK conditions, including column CHECK conditions, using ALTER TABLE DELETE CHECK, and then add in new CHECK conditions.
Deleting a column from a table does not delete CHECK conditions associated with the column that are held in the table constraint. If the constraints are not removed, any attempt to query data in the table produces a column not found error message.