SQL Server ANSI_NULLS , QUOTED_IDENTIFIER

这是 SQL-92 设置语句，使 SQL Server 遵从 SQL-92 规则。

当 SET ANSI_NULLS 为 ON 时，等于 (=) 和不等于 (<>) 比较运算符遵从 SQL-92 标准，对NULL值的操作只能用：

WHERE Column IS NULL / WHERE Column IS NOT NULL

当 SET ANSI_NULLS 为 OFF 时，对NULL值的操作可以用：

WHERE Column = NULL / WHERE Column <> NULL

WHERE Column IS NULL / WHERE Column IS NOT NULL

使用 WHERE Column <> Value 时返回所有不等于 Value 也不等于 NULL 的行；

SET ANSI_NULLS ON; 
WITH T1 AS
	(SELECT 1 AS ID UNION ALL 
	 SELECT NULL UNION ALL 
	 SELECT 2)
SELECT * FROM T1 WHERE ID IS NULL;


SET ANSI_NULLS OFF; 
WITH T1 AS
	(SELECT 1 AS ID UNION ALL 
	SELECT NULL UNION ALL 
	SELECT 2)
SELECT * FROM T1 WHERE ID = NULL;


SET ANSI_NULLS OFF; 
WITH T1 AS
	(SELECT 1 AS ID UNION ALL 
	SELECT NULL UNION ALL 
	SELECT 2)
SELECT * FROM T1 WHERE ID <> 1;

关于NULL的延伸：

1. 对应聚合函数COUNT，只有SELECT COUNT(*)和SELECT COUNT(1) 会将为NULL的行计算在内，SELECT COUNT(ID)会忽略ID列为NULL的行 2. 对应除COUNT外的其他聚合函数，计算时不考虑为NULL的行 3. 对应CHECK CONSTRAINT,如果列允许为NULL的条件下，为NULL的行将不受CHEKC CONSTRAINT的限制，例如有CHECK CONSTRAINT条件为C1>10，对C1列插入NULL值或更新为NULL不会违反CHECK CONSTRAINT. 4. 在GROUP BY ， Distinct 的时候，会将所有NULL归为一组

当 SET QUOTED_IDENTIFIER 为 ON 时，双引号可以代替标识符，单引号表示文本。当 SET QUOTED_IDENTIFIER 为 OFF 时，标识符不可能用双引号代替，单引号，双引号都表示文本。且必须符合所有 Transact-SQL 标识符规则。

-- OFF 时， 不能用引号代替标示符：
SET QUOTED_IDENTIFIER OFF
CREATE TABLE "table name" ("identity" INT  NOT NULL, "order" VARCHAR(100) NOT NULL);


-- ON时， 双引号可以代替标示符[]：
SET QUOTED_IDENTIFIER ON;
CREATE TABLE "table name" ("identity" INT  NOT NULL, "order" VARCHAR(100) NOT NULL);
GO


SELECT "identity","order"  FROM  "table name" ORDER BY "order";


SET QUOTED_IDENTIFIER OFF;
INSERT INTO dbo.[table name] VALUES (1, "'Text in single quotes'");
INSERT INTO dbo.[table name] VALUES (2, '''Text in single quotes''');
INSERT INTO dbo.[table name] VALUES (3, 'Text with 2 '''' single quotes');
INSERT INTO dbo.[table name] VALUES (4, '"Text in double quotes"');
INSERT INTO dbo.[table name] VALUES (5, """Text in double quotes""");
INSERT INTO dbo.[table name] VALUES (6, "Text with 2 """" double quotes");
INSERT INTO dbo.[table name] VALUES (7, 'Text with a single '' quote');
GO


--ON时， 双引号不能用于字符串：
SET QUOTED_IDENTIFIER ON;
INSERT INTO dbo.[table name] VALUES (8, """Text in double quotes""");


SELECT [identity], [order] FROM dbo.[table name];

DROP TABLE dbo.[table name];

参考文档：
http://www.cnblogs.com/TeyGao/p/3521657.html
https://msdn.microsoft.com/zh-cn/library/ms174393.aspx
http://flandycheng.blog.51cto.com/855176/280179

SQL Server ANSI_NULLS , QUOTED_IDENTIFIER

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