Teradata Database verifies that the structure of columns defined as foreign keys, or referenced by foreign keys, is not changed in any manner that violates the rules for the definition of a foreign key constraint.
An ALTER TABLE (or DROP INDEX) request attempting to change the structure of such a column aborts and causes the system to return an error to the requestor.
Teradata Database verifies that a table referenced by another is not dropped. Before dropping the table, you must perform an ALTER TABLE request to drop the foreign key reference.