mysql的触发器不工作的更新查询

Question

我每周参加一个MySQL表..

CREATE TABLE IF NOT EXISTS `students_attendance` (
    `student_id` SMALLINT(5) UNSIGNED ZEROFILL NOT NULL, 
    `month` TINYINT UNSIGNED NOT NULL, 
    `w1` ENUM ('Absent', 'Present', 'Leave') NULL, 
    `w2` ENUM ('Absent', 'Present', 'Leave') NULL, 
    `w3` ENUM ('Absent', 'Present', 'Leave') NULL, 
    `w4` ENUM ('Absent', 'Present', 'Leave') NULL, 
    `w5` ENUM ('Absent', 'Present', 'Leave') NULL, 
    `timestamp` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP, 
    PRIMARY KEY (`student_id`, `month`) 
) ENGINE=InnoDB; 

我使用触发器自动插入新行一个月

DELIMITER $$ 
    CREATE TRIGGER update_students_attendance 
    BEFORE UPDATE ON `students_attendance` FOR EACH ROW 
    begin 
     DECLARE new_month TINYINT; 
     SET new_month = (SELECT month FROM students_attendance WHERE student_id = NEW.student_id AND month = NEW.month); 
     IF new_month is NULL OR new_month = '' 
     THEN 
      INSERT INTO students_attendance (student_id, month) VALUES (NEW.student_id, NEW.month); 
     END IF; 
    END; 
    $$ 
DELIMITER ; 

每但是当我使用低于更新声明，它不插入任何行...

UPDATE students_attendance set `w1` = 'Absent' where `student_id` = '1' and `month` = '1' 

任何人都可以帮助我？

Answer 1

UPDATE students_attendance SET w1='Absent' WHERE student_id='1' AND month='1' 

Answer 2

尝试上面的代码。

Answer 3

请检查下面提到的触发器。

DELIMITER $$ 
    CREATE TRIGGER update_students_attendance 
    BEFORE UPDATE ON `students_attendance` FOR EACH ROW 
    begin 
     DECLARE new_month TINYINT DEFAULT 0; 
     SELECT month into new_month FROM students_attendance WHERE student_id = NEW.student_id AND month = NEW.month; 
     IF new_month is NULL OR new_month < 1 THEN 
      INSERT INTO students_attendance (student_id, month) VALUES (NEW.student_id, NEW.month); 
     END IF; 
    END; 
    $$ 
DELIMITER ;