mysql Integrity constraint violation: 1451 Cannot delete or update a parent row: a foreign key constraint fails code example

Example 1: error 1451 (23000): cannot delete or update a parent row: a foreign key constraint fails

SET FOREIGN_KEY_CHECKS = 0; -- to disable FK checks (ex: for delete purpose)
SET FOREIGN_KEY_CHECKS = 1; -- to re-enable FK checks

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;