cannot delete or update a parent row a foreign key constraint fails in mysql code example

Example 1: mysql cannot delete or update a parent row

# THIS SHOULD ONLY BE USED AS A LAST RESORT
SET FOREIGN_KEY_CHECKS=0; -- to disable them
SET FOREIGN_KEY_CHECKS=1; -- to re-enable them

Example 2: Cannot delete or update a parent row: a foreign key constraint fails (

ALTER TABLE "appointments" DROP FOREIGN KEY "appointments_user_id_foreign";

ALTER TABLE "appointments" ADD CONSTRAINT "appointments_user_id_foreign" FOREIGN KEY ("user_id") REFERENCES "users" ("id") ON DELETE CASCADE;