sql高手请进~~~（exists和赋值的问题）

[doyouknowm]

declare @ID bigint
if exists (select @ID=ID
from dbo.T_D_TA_WareHouseIn
where
MakerItemCD=@MakerItemCD and
Amount=@Amount and
MakeDate=@MakeDate and
BoxNo=@BoxNo and
UseFlag=' ')
为什么加上@ID就不对呢，赋值的时候不能和exists共用还是怎么回事啊，帮帮忙啊

[doyouknowm]

另：后面的变量都是定义过的

[freeliu]

我想exist后面不能跟赋值吧。

[dawugui]

declare @ID bigint
select @ID=ID
from dbo.T_D_TA_WareHouseIn
where
MakerItemCD=@MakerItemCD and
Amount=@Amount and
MakeDate=@MakeDate and
BoxNo=@BoxNo and
UseFlag=' ')
if @ID is null then print '不存在' else print cast(@ID as varchar)

[doyouknowm]

谢谢老乌龟了，解决^-^