问题描述
这是关于我在 Microsoft Sql Server 中发现的一个奇怪的行为.如果我错了,请纠正我.
This is about a bizarre behaviour I found in Microsoft Sql Server. Please correct me if I'm wrong.
SELECT COUNT(*) FROM TABLEA
WHERE [Column1] IS NULL;
这将返回 30018 行.
This returns 30018 rows.
CREATE VIEW VIEWB AS
SELECT * FROM TABLEA AS t1
WHERE t1.[Column1] NOT IN ('Cross/Up sell', 'Renegotiation', 'Renewal')
如果我检查VIEWB
,我在Column1
中找不到NULL
:
If I check VIEWB
, I don't find NULL
in Column1
:
SELECT COUNT(*) FROM VIEWB
WHERE [Column1] IS NULL;
这将返回 0 行.
为什么?上面的查询排除了 3 个值,但不应该排除 NULL.为什么 Ms Sql Server 会这样?我应该预料到这一点吗?我该如何解决?
Why? The query above excludes the 3 values, but it isn't supposed to exclude NULL. Why does Ms Sql Server behave this way? Should I have expected this?How can I fix it?
推荐答案
这实际上是 SQL Server 将 NULL 视为值时常见的错误.默认情况下,它被视为未知,如此处所述.因此,在您看来,您还需要包含一个 OR t1.[Column1] IS NULL
.
This is actually a common mistake made with SQL Server in treating NULL as a value. By default, it's treated as UNKNOWN, as documented here. So, in your view, you also need to include an OR t1.[Column1] IS NULL
.
您可以通过调用 SET ANSI_NULLS OFF
来更改此行为.但是,不建议使用此功能,因为正如@Martin Smith 所指出的那样,该功能已被弃用.
You can change this behavior by calling SET ANSI_NULLS OFF
. It is not recommended to use this, however, as the feature is deprecated as pointed out by @Martin Smith.
然而,这不是 SQL Server 特定的问题.它是 ANSI SQL 标准的一部分.
This is not a SQL Server specific issue, however. It's part of the ANSI SQL standard.
这篇关于NULL 值被排除在外.为什么?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!