Question

CREATE TABLE parent (id INT NOT NULL,
                     PRIMARY KEY (id)
) ENGINE=INNODB;


CREATE TABLE child (id INT, parent_id INT,
                    INDEX par_ind (parent_id),
                    FOREIGN KEY (parent_id) REFERENCES parent(id)
                      ON DELETE CASCADE
) ENGINE=INNODB;

I dont understand the meaning of putting ENGINE = INNODB here, and why do we use ON DELETE CASCADE?

Answer 1

engine=innodb will ensure you get foreign key support. The default MyISAM engine doesn’t support foreign keys. On delete cascade will remove the child row if the referenced row in the parent table is removed.