批量更新数据小心SQL触发器的陷阱

批量更新数据时候，Inserted和Deleted临时表也是批量的，但触发器只会调用执行一次！两个概念千万不要弄混淆！

错误的理解；例如：创建在A表上创建了一个Update触发器，里面写的是Update一条记录；当在A表进行update数据时候，会调用执行触发器一次，不可能因为触发器中有Update语句会又执行一次，那样岂不是死循环了。。

本文章转载：http://blog.csdn.net/baronyang/article/details/5174734

原来update触发器只会被update触发一次，无论更新的记录数是多少，以下为验证代码

CREATE TABLE TMP_TABLE1 (PersonCode VARCHAR(20) NOT NULL PRIMARY KEY,[NAME] VARCHAR(50) NULL,DepCode VARCHAR(20) NULL,Amount MONEY null)
CREATE TABLE TMP_TABLE2 (PersonCode VARCHAR(20) NOT NULL PRIMARY KEY,[NAME] VARCHAR(50) NULL,DepCode VARCHAR(20) NULL,Amount MONEY null)

GO
INSERT INTO TMP_TABLE1(PersonCode,[NAME],Amount)
VALUES('00001','AAA1',1000)
INSERT INTO TMP_TABLE1(PersonCode,[NAME],Amount)
VALUES('00002','AAA2',1000)
INSERT INTO TMP_TABLE1(PersonCode,[NAME],Amount)
VALUES('00003','AAA3',1000)
INSERT INTO TMP_TABLE1(PersonCode,[NAME],Amount)
VALUES('00004','AAA4',1000)
INSERT INTO TMP_TABLE1(PersonCode,[NAME],Amount)
VALUES('00005','AAA5',1000)

INSERT INTO TMP_TABLE2(PersonCode,[NAME],Amount)
VALUES('00001','AAA1',1000)
INSERT INTO TMP_TABLE2(PersonCode,[NAME],Amount)
VALUES('00002','AAA2',1000)
INSERT INTO TMP_TABLE2(PersonCode,[NAME],Amount)
VALUES('00003','AAA3',1000)
INSERT INTO TMP_TABLE2(PersonCode,[NAME],Amount)
VALUES('00004','AAA4',1000)
INSERT INTO TMP_TABLE2(PersonCode,[NAME],Amount)
VALUES('00005','AAA5',1000)

GO
Alter TRIGGER dbo.tmp_table1_update ON tmp_table1
AFTER UPDATE
AS
SELECT * INTO #INS FROM INSERTED
DECLARE @PersonCode VARCHAR(20),@Amount MONEY
IF UPDATE(Amount)
BEGIN
  SELECT @personcode=personcode,@Amount=Amount FROM #INS
  UPDATE TMP_TABLE2 SET Amount =@Amount WHERE PersonCode=@PersonCode	
END

GO

UPDATE TMP_TABLE1 SET Amount = 2000
select * from TMP_TABLE1
SELECT * FROM TMP_TABLE2

　　

然后再更新,发现TMP_TABLE1的Amount字段值都更新为2000，但TMP_TABLE2的Amount值只有第一条记录更新了，下面改一下触发器

Alter TRIGGER dbo.tmp_table1_update ON tmp_table1
AFTER UPDATE
AS
SELECT * INTO #INS FROM INSERTED
DECLARE @PersonCode VARCHAR(20),@Amount MONEY
IF UPDATE(Amount)
BEGIN
	DECLARE AmountCursor CURSOR FOR
	SELECT personcode,Amount FROM #INS
	OPEN AmountCursor
	FETCH NEXT FROM AmountCursor INTO @PersonCode,@Amount
	WHILE @@FETCH_STATUS=0
	BEGIN
		UPDATE TMP_TABLE2 SET Amount =@Amount WHERE PersonCode=@PersonCode
		FETCH NEXT FROM AmountCursor INTO @PersonCode,@Amount
	END
	CLOSE AmountCursor
	DEALLOCATE AmountCursor			
END

　　

更新触发器后，一些正常。

总结：为了保险起见，update触发器还是要用游标来处理，才能保证全部触发执行.