How to add 'ON DELETE CASCADE' in ALTER TABLE statement
As explained before:
ALTER TABLE TABLEName
drop CONSTRAINT FK_CONSTRAINTNAME;
ALTER TABLE TABLENAME
ADD CONSTRAINT FK_CONSTRAINTNAME
FOREIGN KEY (FId)
REFERENCES OTHERTABLE
(Id)
ON DELETE CASCADE ON UPDATE NO ACTION;
As you can see those have to be separated commands, first dropping then adding.
You can not add ON DELETE CASCADE
to an already existing constraint. You will have to drop
and re-create
the constraint. The documentation shows that the MODIFY CONSTRAINT
clause can only modify the state of a constraint (i-e: ENABLED/DISABLED
...).
First drop
your foreign key and try your above command, put add constraint
instead of modify constraint
.
Now this is the command:
ALTER TABLE child_table_name
ADD CONSTRAINT fk_name
FOREIGN KEY (child_column_name)
REFERENCES parent_table_name(parent_column_name)
ON DELETE CASCADE;