Recreate foreign key
--Drop fk
ALTER TABLE favourite_food DROP FOREIGN KEY fk_fav_food_person_id;
--Alter your pk
ALTER TABLE person modify person_id smallint unsigned auto_increment;
--Recreate fk
ALTER TABLE favourite_food ADD CONSTRAINT fk_fav_food_person_id FOREIGN KEY (person_id) REFERENCES person (person_id) ON DELETE CASCADE;