NULLIF（）函数不适用于WHERE子句

Question

以下Query的实际结果为NULL

select semid from programvariantterm where programvariantid = 240

但是当我尝试以下语句时，它会给出0行：

declare @semid int
set @semid = -1
select semid from programvariantterm 
where programvariantid = 240 and semid = nullif(@semid,-1)

Answer 1

我认为你有点混淆NULLIF和ISNULL。

您的陈述适用于以下ISNULL：

where programvariantid = 240 and @semid = ISNULL(semid,-1)