sql server not in 查询没结果

今天使用SQL Server 时，遇到使用not in 和not exist的查询结果有差异：not in 查询没结果。

原因：not in 遇到null就不工作了。

摘录：

SELECT foreignStockId FROM[Subset].[dbo].[Products]

Probably returns a NULL. Try

SELECT stock.IdStock ,stock.Descr FROM[Inventory].[dbo].[Stock] stock WHERE stock.IdStock NOTIN(SELECT foreignStockId FROM[Subset].[dbo].[Products]WHERE foreignStockId ISNOTNULL)

a NOT IN (x,y,NULL) Will always return no results as it is equivalent to

a<>x and a<>y and a<>NULL which is

true and true and unknown

Which evaluates to unknown under the rules of three valued logic.

I normally use NOT EXISTS for this type of query

SELECT stock.idstock, stock.descr FROM[Inventory].[dbo].[Stock] stock WHERENOTEXISTS(SELECT*FROM[Subset].[dbo].[Products] p WHERE p.foreignstockid = stock.idstock)

原文网址：

http://stackoverflow.com/questions/5231712/sql-not-in-not-working