写一个mysql触发器a表有u、c、s三列当更新s列为2时将u列和c列的值调换再向a表插入一行

DELIMITER $$ CREATE TRIGGER swap_u_c AFTER UPDATE ON a FOR EACH ROW BEGIN IF NEW.s = 2 THEN SET @temp_u = NEW.u; SET NEW.u = NEW.c; SET NEW.c = @temp_u; INSERT INTO a(u, c, s) VALUES (NEW.u, NEW.c, NEW.s); END IF; END$$ DELIMITER ;