比较可以包含NULL的列-有没有更优雅的方法？

我知道您不能将值与NULL进行比较，而不能在不添加以下代码的情况下期望结果...

SELECT
    *
FROM 
    A INNER JOIN 
    B ON A.ID = B.ID
WHERE
    A.STRING <> B.STRING OR (A.STRING IS NULL AND B.STRING IS NOT NULL) OR (A.STRING IS NOT NULL AND B.STRING IS NULL) OR 
    A.DT <> B.DT OR (A.DT IS NULL AND B.DT IS NOT NULL) OR (A.DT IS NOT NULL AND B.DT IS NULL) OR 
    A.B <> B.B OR (A.B IS NULL AND B.B IS NOT NULL) OR (A.B IS NOT NULL AND B.B IS NULL) OR 
    A.NUM <> B.NUM OR (A.NUM IS NULL AND B.NUM IS NOT NULL) OR (A.NUM IS NOT NULL AND B.NUM IS NULL) 

我的问题是：

有没有一种更优雅的方法来测试两个表中任何一个都可能为null的值的变化？

解决方案需要跨数据类型统一工作。

这是设置测试表的代码...

CREATE TABLE A
(
    ID INT IDENTITY(1,1) NOT NULL,
    STRING VARCHAR(20) NULL,
    DT DATETIME NULL,
    B BIT NULL,
    NUM INT NULL
)

CREATE TABLE B
(
    ID INT IDENTITY(1,1) NOT NULL,
    STRING VARCHAR(20) NULL,
    DT DATETIME NULL,
    B BIT NULL,
    NUM INT NULL
)


INSERT INTO A (STRING, DT, B, NUM) VALUES ('TEST', '2012-03-16 16:39:04.893', 0, 23)
INSERT INTO A (STRING, DT, B, NUM) VALUES (NULL, '2012-03-16 16:39:04.893', 0, 23)
INSERT INTO A (STRING, DT, B, NUM) VALUES ('TEST', NULL, 0, 23)
INSERT INTO A (STRING, DT, B, NUM) VALUES ('TEST', '2012-03-16 16:39:04.893', NULL, 23)
INSERT INTO A (STRING, DT, B, NUM) VALUES ('TEST', '2012-03-16 16:39:04.893', 0, NULL)
INSERT INTO A (STRING, DT, B, NUM) VALUES ('TEST', '2012-03-16 16:39:04.893', 0, 23)
INSERT INTO A (STRING, DT, B, NUM) VALUES ('TEST', '2012-03-16 16:39:04.893', 0, 23)
INSERT INTO A (STRING, DT, B, NUM) VALUES ('TEST', '2012-03-16 16:39:04.893', 0, 23)
INSERT INTO A (STRING, DT, B, NUM) VALUES ('TEST', '2012-03-16 16:39:04.893', 0, 23)
INSERT INTO A (STRING, DT, B, NUM) VALUES ('TEST', '2012-03-16 16:39:04.893', 0, 23)


INSERT INTO B (STRING, DT, B, NUM) VALUES ('TEST', '2012-03-16 16:39:04.893', 0, 23)
INSERT INTO B (STRING, DT, B, NUM) VALUES ('TEST', '2012-03-16 16:39:04.893', 0, 23)
INSERT INTO B (STRING, DT, B, NUM) VALUES ('TEST', '2012-03-16 16:39:04.893', 0, 23)
INSERT INTO B (STRING, DT, B, NUM) VALUES ('TEST', '2012-03-16 16:39:04.893', 0, 23)
INSERT INTO B (STRING, DT, B, NUM) VALUES ('TEST', '2012-03-16 16:39:04.893', 0, 23)
INSERT INTO B (STRING, DT, B, NUM) VALUES ('STAGE', '2012-03-16 16:39:04.893', 0, 23)
INSERT INTO B (STRING, DT, B, NUM) VALUES ('TEST', '2555-11-11 00:00:00.000', 0, 23)
INSERT INTO B (STRING, DT, B, NUM) VALUES ('TEST', '2012-03-16 16:39:04.893', 0, 23)
INSERT INTO B (STRING, DT, B, NUM) VALUES ('TEST', '2012-03-16 16:39:04.893', 0, 23)
INSERT INTO B (STRING, DT, B, NUM) VALUES ('TEST', '2012-03-16 16:39:04.893', 0, 999)

您可以在Paul White的文章《未记录的查询计划：平等比较》中使用这种方法。

SELECT * 
FROM   A 
       INNER JOIN B 
         ON A.ID = B.ID 
            AND EXISTS(SELECT A.* 
                       EXCEPT 
                       SELECT B.*) 

在SQL Server 2005及更高版本中受支持的标准SQL：

WITH A_MINUS_B 
     AS
     (
      SELECT * 
        FROM A
      EXCEPT 
      SELECT *
        FROM B
     )
SELECT * 
  FROM A_MINUS_B AS T 
       JOIN B ON T.ID = B.ID;

这是一种全局方法，因此我没有从问题中重写更正的查询。我只是想分享一个有用的点，也许会有所帮助，所以下面的脚本将检查Column1和Column2是否相等，此外，还可以使用Conversion to VARBINARY比较大小写，如果不需要，可以将其删除。

--c1 = Length of Column1
--c2 = Length of Column2

ISNULL(NULLIF(CONVERT(VARBINARY(cl), LTRIM(RTRIM(Column1))),
              CONVERT(VARBINARY(c2), LTRIM(RTRIM(Column2)))),
       NULLIF(CONVERT(VARBINARY(c2), LTRIM(RTRIM(Column2))),
              CONVERT(VARBINARY(c1), LTRIM(RTRIM(Column1))))) IS NULL

您可以将表达式的结尾更改IS NOT NULL为检查不相等条件。

希望能有所帮助。