3
我只是在SQL Server中处理NULL值(在版本12.0.5000.0上测试过)。基本上,我的意图是获得列值为一个静态值(例如999)的所有行。我不是在寻找替代LIKE“使用ISNULL函数”。查询由第三方引擎生成,我不打算编写解析器并更改语句。当ANSI_NULLS被关闭时,T-SQL /意外的NULL处理
-- All examples with ANSI_NULLS OFF
SET ANSI_NULLS OFF;
GO
--------------------------------------------------------------------------------------------------------
-- "Virtual" example/working as expected
--------------------------------------------------------------------------------------------------------
DECLARE
@One INT = 1,
@Null INT = NULL
SELECT
IIF(@Null = NULL, 1, 0) '@Null = NULL' -- To test if ANSI_NULL is OFF
,IIF(@One <> NULL, 1, 0) '@One <> NULL' -- working with NULL variable
,IIF(1 <> NULL, 1, 0) '1 <> NULL' -- working with NULL value
--------------------------------------------------------------------------------------------------------
-- MSDN Example/NOT working as expected
-- https://docs.microsoft.com/en-us/sql/t-sql/statements/set-ansi-nulls-transact-sql
--------------------------------------------------------------------------------------------------------
-- Create table t1 and insert values.
CREATE TABLE dbo.t1 (a INT NULL);
INSERT INTO dbo.t1 values (NULL),(0),(1);
GO
-- SET ANSI_NULLS to OFF and test.
DECLARE @varname int;
SET @varname = 999;
SELECT a
FROM t1
WHERE a <> @varname; -- working with NULL variable
SELECT a
FROM t1
WHERE a <> 999; -- NOT working with NULL value
-- Drop table t1.
DROP TABLE dbo.t1;
任何人都可以解释为什么“虚拟”的例子是以不同的方式工作,然后MSDN的例子?
Virtual example:
+--------------+--------------+-----------+
| @Null = NULL | @One <> NULL | 1 <> NULL |
+--------------+--------------+-----------+
| 1 | 1 | 1 |
+--------------+--------------+-----------+
MSDN example:
-- SELECT 1
+------+
| a |
+------+
| NULL |
| 0 |
| 1 |
+------+
-- SELECT 2
+------+
| a |
+------+
| 0 |
| 1 |
+------+
嘿,小伙子,谢谢你的回答。不是我期望/希望阅读但听起来像我必须找到另一个解决方案;-) – MBauer