插入前如何终止MySQL触发器？
为此，语法如下-
delimiter // create trigger yourTriggerName before insert on yourTableName FOR EACH ROW BEGIN yourStatement1 . . N END // delimiter ;
要了解上述语法，让我们创建一个表-
mysql> create table DemoTable1919 ( Value int );
这是在插入之前创建MySQL触发器的查询-
mysql> delimiter //
mysql> create trigger sumis60 before insert on DemoTable1919
FOR EACH ROW
BEGIN
declare custom_message varchar(256);
IF (SELECT sum(Value) from DemoTable1919) = 60 THEN
set custom_message= "cannot insert because sum(Value) is greater than 60";
signal sqlstate '13500'
set message_text= custom_message;
END IF;
END
//
mysql> delimiter ;现在您可以使用insert命令在表中插入一些记录，并检查触发器的工作情况-
mysql> insert into DemoTable1919 values(10); mysql> insert into DemoTable1919 values(20); mysql> insert into DemoTable1919 values(30); mysql> insert into DemoTable1919 values(40); ERROR 1644 (13500): cannot insert because sum(Value) is greater than 60