如果删除语句使行数低于 2000,我想撤消它:
CREATE TRIGGER Trig1
AFTER DELETE ON Tab1
FOR EACH ROW
IF (SELECT COUNT(*) FROM Table1) < 2000
BEGIN
INSERT INTO Table1 (select * from old);
END;
END IF;
但它不起作用。有人可以告诉我我做错了什么,这应该是什么样子?
尝试,
INSERT INTO Table1
SELECT *
FROM old
要记住的点
*
BEFORE DELETE
如果操作会导致记录太少,则通过创建引发错误(从而导致语句中止)的触发器会更好:
DELIMITER ;;
CREATE TRIGGER foo BEFORE DELETE ON Table1 FOR EACH ROW
IF (SELECT COUNT(*) FROM Table1) <= 2000 THEN SIGNAL SQLSTATE '45000' SET
MESSAGE_TEXT = 'Cannot delete when table would result in too few records';
END IF;;
DELIMITER ;
请注意,SIGNAL
仅在 MySQL 5.5 中引入。如果使用较早的版本,则必须改为强制 MySQL 通过执行错误操作引发异常;我经常CALL
使用例如不存在的程序CALL raise_error;
。
你可以试试这段代码:
DELIMITER $$
DROP TRIGGER IF EXISTS `Trig1`$$
CREATE TRIGGER `Trig1`
AFTER DELETE ON Table1
FOR EACH ROW
BEGIN
IF (SELECT COUNT(*) FROM Table1) < 2000 THEN
INSERT INTO Table2(field1, field2, field3) VALUES(old.field1, old.field2, old.field3);
END IF;
END$$
DELIMITER ;
我实际上已经对其进行了测试,并且它适用于我。