NULLIF（）函數不與WHERE子句

Question

以下查詢的實際結果是NULL工作

select semid from programvariantterm where programvariantid = 240 

但是當我嘗試下面的語句，它給0行：

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

Answer 1

我認爲你有點混淆NULLIF和ISNULL。

你的聲明將與以下ISNULL工作：

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