Modifying and deleting CHECK conditions

There are several ways to alter the existing set of CHECK conditions on a table.

ALTER TABLE office
MODIFY city
CHECK ( city IN ( 'city_1', 'city_2', 'city_3' ) )

There are two ways of modifying a CHECK condition defined on the table, as opposed to a CHECK condition defined on a column.

All CHECK conditions on a table, including CHECK conditions on all its columns and CHECK conditions inherited from user-defined data types, are removed using the ALTER TABLE statement with the DELETE CHECK clause, as follows:

ALTER TABLE table_name
DELETE CHECK

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.