MySQL触发器使用过程详解

DELIMITER //
CREATE TRIGGER before_insert_test_tri
BEFORE INSERT ON test_trigger
FOR EACH ROW 
BEGIN
INSERT INTO test_trigger_log(t_node)
VALUES('before insert');
END //
DELIMITER ;
INSERT INTO test_trigger(t_node)
VALUES('test..');
SELECT * FROM test_trigger;
SELECT * FROM test_trigger_log;

DELIMITER //
CREATE TRIGGER salary_check_trigger
BEFORE INSERT ON emp
FOR EACH ROW
BEGIN
	DECLARE mgr_sal DOUBLE;
	SELECT salary INTO mgr_sal FROM emp
	WHERE employee_id = NEW.manager_id;
	IF NEW.salary > mgr_sal
		THEN SIGNAL SQLSTATE 'HY000' SET MESSAGE_TEXT = '薪资不得高于领导薪资';
	END IF;
END //
DELIMITER ;
DESC emp;
INSERT INTO emp(employee_id,last_name,email,hire_date,job_id,salary,manager_id)
VALUES(300,'test','tom@126.com',CURDATE(),'AD_VP',10000,103);

mysql> SHOW TRIGGERS\G;
*************************** 1. row ***************************
             Trigger: salary_check_trigger
               Event: INSERT
               Table: emp
           Statement: BEGIN
	DECLARE mgr_sal DOUBLE;
	SELECT salary INTO mgr_sal FROM emp
	WHERE employee_id = NEW.manager_id;
	IF NEW.salary > mgr_sal
		THEN SIGNAL SQLSTATE 'HY000' SET MESSAGE_TEXT = '薪资不得高于领导薪资';
	END IF;
END
              Timing: BEFORE
             Created: 2023-02-28 15:46:44.71
            sql_mode: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
             Definer: root@%
character_set_client: utf8
collation_connection: utf8_general_ci
  Database Collation: utf8_general_ci

SHOW CREATE TRIGGER salary_check_trigger\G;

SELECT * FROM information_schema.TRIGGERS\G;

DROP TRIGGER salary_check_trigger