On delete cascade to table

Question

How can I add on delete cascade to this table creation script? id_fk comes from mytable table.

 CREATE TABLE IF NOT EXISTS `ip` (

  `ip_id` int(11) NOT NULL AUTO_INCREMENT,

  `id_fk` int(11) DEFAULT NULL,

  `ip_add` varchar(40) DEFAULT NULL,

  PRIMARY KEY (`ip_id`),

  KEY `id_fk` (`id_fk`)

) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1;

Answer 1

Add a foreign key constraint and specify what to do and when.

 ALTER TABLE ip
    ADD CONSTRAINT constraint_name
        FOREIGN KEY index_name(id_fk)
            REFERENCES other_table(other_column_name)
                ON DELETE CASCADE
                ON UPDATE CASCADE;

You can include the constraint directly in the table definition:

FOREIGN KEY index_name(id_fk)
    REFERENCES other_table(other_column_name)
        ON DELETE CASCADE
        ON UPDATE CASCADE;

Answer 2

Try this:

ALTER TABLE `ip`
ADD CONSTRAINT `FK_mytable` FOREIGN KEY (`id_fk`) REFERENCES `mytable` (`id`)   
ON DELETE CASCADE ON UPDATE CASCADE;

Hope this helps!