mysql中的trigger

mysql中trigger的语法跟procedure和function类似。
1 创建

    CREATE[DEFINER = { user | CURRENT_USER }]TRIGGER trigger_nametrigger_time trigger_eventON tbl_name FOR EACH ROWtrigger_bodytrigger_time: { BEFORE | AFTER }trigger_event: { INSERT | UPDATE | DELETE }

具体操作中也和function类似，例如：

    mysql> delimiter //mysql> CREATE TRIGGER upd_check BEFORE UPDATE ON account-> FOR EACH ROW-> BEGIN->     IF NEW.amount < 0 THEN->         SET NEW.amount = 0;->     ELSEIF NEW.amount > 100 THEN->         SET NEW.amount = 100;->     END IF;-> END;//mysql> delimiter ;

MySQL alter，若只有一句trigger语句，则begin...end复合句式可以不用，如：

    mysql> CREATE TRIGGER ins_sum BEFORE INSERT ON account-> FOR EACH ROW SET @sum = @sum + NEW.amount;

不同的地方是：
a trigger不能用call来调用
b trigger的语句中不能有事务的开启和结束，如 START TRANSACTION, COMMIT, or ROLLBACK等等。
2 查看trigger

    SHOW TRIGGERS [{FROM | IN} db_name][LIKE 'pattern' | WHERE expr]或者从information_schema.TRIGGERS中查看SELECT * FROM INFORMATION_SCHEMA.TRIGGERSWHERE condition;

3 删除

    DROP TRIGGER [IF EXISTS] [schema_name.]trigger_name