SET ANSI_NULLS ON

指定在与 Null 值一起使用等于 (=) 和不等于 (<>) 比较运算符时采用符合 ISO 标准的行为。

当 SET ANSI_NULLS 为 ON 时，即使 column_name 中包含空值，使用 WHERE column_name = NULL 的 SELECT 语句仍返回零行。即使 column_name 中包含非空值，使用 WHERE column_name <> NULL 的 SELECT 语句仍会返回零行。

当 SET ANSI_NULLS 为 OFF 时，等于 (=) 和不等于 (<>) 比较运算符不遵守 ISO 标准。使用 WHERE column_name = NULL 的 SELECT 语句返回 column_name 中包含空值的行。使用 WHERE column_name <> NULL 的 SELECT 语句返回列中包含非空值的行。

 

例子：

 -- Create table t1 and insert values.
CREATE TABLE t1 (a INT NULL,b VARCHAR(40))
INSERT INTO t1 values (NULL,'HH')
INSERT INTO t1 values (0,'LL')
INSERT INTO t1 values (1,'OO')
GO

1、

-- Print message and perform SELECT statements.
PRINT 'Testing default setting';
DECLARE @varname int;
SELECT @varname = NULL;
SELECT * FROM t1 WHERE a = @varname;
SELECT * FROM t1 WHERE a <> @varname;
SELECT * FROM t1 WHERE a IS NULL;
GO

输出：

 

Testing default setting
a           b
----------- ----------------------------------------
NULL        HH

(1 row(s) affected)

a           b
----------- ----------------------------------------
0           LL
1           OO

(2 row(s) affected)

a           b
----------- ----------------------------------------
NULL        HH

(1 row(s) affected)

 

2、

-- SET ANSI_NULLS to ON and test.
PRINT 'Testing ANSI_NULLS ON'
SET ANSI_NULLS ON
GO
DECLARE @varname int;
SELECT @varname = NULL;
SELECT * FROM t1 WHERE a = @varname;
SELECT * FROM t1 WHERE a <> @varname;
SELECT * FROM t1 WHERE a IS NULL;
GO

输出：

 

Testing ANSI_NULLS ON
a           b
----------- ----------------------------------------

(0 row(s) affected)

a           b
----------- ----------------------------------------

(0 row(s) affected)

a           b
----------- ----------------------------------------
NULL        HH

(1 row(s) affected)

 

3、

-- SET ANSI_NULLS to OFF and test.
PRINT 'Testing SET ANSI_NULLS OFF';
SET ANSI_NULLS OFF;
GO
DECLARE @varname int;
SELECT @varname = NULL;
SELECT * FROM t1 WHERE a = @varname;
SELECT * FROM t1 WHERE a <> @varname;
SELECT * FROM t1 WHERE a IS NULL;
GO

输出：

 

Testing SET ANSI_NULLS OFF
a           b
----------- ----------------------------------------
NULL        HH

(1 row(s) affected)

a           b
----------- ----------------------------------------
0           LL
1           OO

(2 row(s) affected)

a           b
----------- ----------------------------------------
NULL        HH

(1 row(s) affected)

Fighting

 

 

转自： http://www.cnblogs.com/cry/archive/2009/03/26/1422309.html