Ошибка: #1362 - Updating of NEW row is not allowed in after trigger

Пытаюсь написать два триггера, проверяющие целостность данных при вставке и изменении данных в PHPMyAdmin

Выдает ошибку: #1362 - Updating of NEW row is not allowed in after trigger

DROP TRIGGER IF EXISTS `students_constraints_insert` ;
delimiter ||
CREATE TRIGGER `students_constraints_insert` BEFORE INSERT ON `Students`
FOR EACH
ROW BEGIN
IF not(NEW.kurs >=1 and NEW.kurs <= 6) THEN
SET NEW.kurs = 0;
END IF; 
IF not(NEW.spec >= 'А' AND NEW.spec <= 'я') THEN
SET NEW.spec = 0;
END IF;
IF not(NEW.gr >='01' AND NEW.gr <= '99') THEN
SET NEW.gr = 0;
END IF;
END ||
delimiter ;
DROP TRIGGER IF EXISTS `students_constraints_update` ;
delimiter ||
CREATE TRIGGER `students_constraints_update` AFTER UPDATE ON `Students`
FOR EACH
ROW BEGIN
IF not(NEW.kurs >=1 and NEW.kurs <= 6) THEN
SET NEW.kurs = 0;
END IF; 
IF not(NEW.spec >= 'А' AND NEW.spec <= 'я') THEN
SET NEW.spec = 0;
END IF;
IF not(NEW.gr >='01' AND NEW.gr <= '99') THEN
SET NEW.gr = 0;
END IF;
END ||
delimiter ;