SQL查询每行中最大值的技巧

--------------------------------------------------------------------------

-- Author : htl258(Tony)

-- Date : 2010-04-23 08:08:36

-- Version:Microsoft SQL Server 2008 (RTM) - 10.0.1600.22 (Intel X86)

-- Jul 9 2008 14:43:34

-- Copyright (c) 1988-2008 Microsoft Corporation

-- Developer Edition on Windows NT 5.1 <X86> (Build 2600: Service Pack 3)

-- Blog : http://blog.csdn.net/htl258

-- Subject: SQL查询每行中最大值的技巧

--------------------------------------------------------------------------

--> 生成测试数据表:tb

IF NOT OBJECT_ID('[tb]') IS NULL

DROP TABLE [tb]

GO

CREATE TABLE [tb](

a SMALLINT,

b SMALLINT,

c SMALLINT,

d SMALLINT,

e SMALLINT,

f SMALLINT,

g SMALLINT

)

INSERT [tb]

SELECT 1,2,3,4,5,2,3 UNION ALL

SELECT 4,5,6,7,7,2,0 UNION ALL

SELECT 4,9,6,7,7,9,6

GO

--SELECT * FROM [tb]

-->SQL查询如下:

SELECT *,

(SELECT MAX(a)

FROM(

SELECT a UNION ALL

SELECT b UNION ALL

SELECT c UNION ALL

SELECT d UNION ALL

SELECT e UNION ALL

SELECT f UNION ALL

SELECT g

) AS t

) AS maxvalue

FROM tb

/*

a b c d e f g maxvalue

------ ------ ------ ------ ------ ------ ------ --------

1 2 3 4 5 2 3 5

4 5 6 7 7 2 0 7

4 9 6 7 7 9 6 9

(3 行受影响)

*/