MSSQL多列取最大或者最小值

/*

lvl1 lvl2 lvl3 lvl4 lvl
4 3 4 1
3 2 2 1
2 2 3 4
4 4 3 4
3 1 2 2
怎么写代码 去比较lvl1、lvl2、lvl3、lvl4 对应每行的值，取其中最小的，将其值添加到lvl列里
运行结果应该是
lvl
1
1
2
3
1

*/

--方法(一) 函數法

-->Title:Generating test data
-->Author:wufeng4552
-->Date :2009-10-16 09:58:16

if not object_id('Tempdb..#t') is null
drop table #t
Go
Create table #t([lvl1] int,[lvl2] int,[lvl3] int,[lvl4] int,[lvl] int)
Insert #t
select 4,3,4,1,null union all
select 3,2,2,1,null union all
select 2,2,3,4,null union all
select 4,4,3,4,null union all
select 3,1,2,2,null
Go
if object_id('UF_minget')is not null drop function UF_minget
go
create function UF_minget
(@col1 int,@col2 int,@col3 int,@col4 int)
returns int
as
begin
declare @t table(col int)
insert @t select @col1 union all
select @col2 union all
select @col3 union all
select @col4
return(select min(col)from @t)
end
go
update t set [lvl]=dbo.UF_minget([lvl1],[lvl2],[lvl3],[lvl4])
from #t t
select * from #t
/*
lvl1 lvl2 lvl3 lvl4 lvl
----------- ----------- ----------- ----------- -----------
4 3 4 1 1
3 2 2 1 1
2 2 3 4 2
4 4 3 4 3
3 1 2 2 1

(5 個資料列受到影響)


*/

--方法二 MSSQL2005 XML PATH

-------------------------------------
-- Author : liangCK 梁爱兰
-- Comment: 小梁 爱 兰儿
-- Date : 2009-10-16 09:57:38
-------------------------------------

--> 生成测试数据: @T
DECLARE @T TABLE (lvl1 int,lvl2 int,lvl3 int,lvl4 int,lvl int)
INSERT INTO @T
SELECT 4,3,4,1,null UNION ALL
SELECT 3,2,2,1,null UNION ALL
SELECT 2,2,3,4,null UNION ALL
SELECT 4,4,3,4,null UNION ALL
SELECT 3,1,2,2,null

--SQL查询如下:

UPDATE A SET
lvl = B.x.value('min(//row/*)','int')
FROM @T AS A
CROSS APPLY (SELECT x = (SELECT A.* FOR XML PATH('row'),TYPE)) AS B;

SELECT * FROM @T;

/*
lvl1 lvl2 lvl3 lvl4 lvl
----------- ----------- ----------- ----------- -----------
4 3 4 1 1
3 2 2 1 1
2 2 3 4 2
4 4 3 4 3
3 1 2 2 1

(5 行受影响)

*/
--方法(三) 作者 (四方城)

if object_id('[tb]') is not null drop table [tb]
go
create table [tb]([lvl1] int,[lvl2] int,[lvl3] int,[lvl4] int,[lvl] int)
insert [tb]
select 4,3,4,1,null union all
select 3,2,2,1,null union all
select 2,2,3,4,null union all
select 4,4,3,4,null union all
select 3,1,2,2,null
go

create function getmin(@a varchar(8000))
returns int
as
begin declare @ table (id int identity,a char(1))
declare @t int
insert @ select top 8000 null from sysobjects a,sysobjects b
select @t=min(cast(substring(','+@a,id+1,charindex(',',','+@a+',',id+1)-id-1) as int))
from @ where substring(','+@a,id,8000) like ',_%'
return @t
end
go

-->查询
select
lvl1,
lvl2,
lvl3,
lvl4,
lvl=dbo.getmin(ltrim(lvl1)+','+ltrim(lvl2)+','+ltrim(lvl3)+','+ltrim(lvl4))
from tb

/**
lvl1 lvl2 lvl3 lvl4 lvl
----------- ----------- ----------- ----------- -----------
4 3 4 1 1
3 2 2 1 1
2 2 3 4 2
4 4 3 4 3
3 1 2 2 1

(5 行受影响)
**/

--方法(四)

-->Title:Generating test data
-->Author:wufeng4552
-->Date :2009-10-16 09:58:16

if not object_id('Tempdb..#t') is null
drop table #t
Go
Create table #t([lvl1] int,[lvl2] int,[lvl3] int,[lvl4] int,[lvl] int)
Insert #t
select 4,3,4,1,null union all
select 3,2,2,1,null union all
select 2,2,3,4,null union all
select 4,4,3,4,null union all
select 3,1,2,2,null
Go

if object_id('UF_minget')is not null drop function UF_minget
go
create function UF_minget
(@s varchar(200))
returns int
as
begin
return(
select col=min(substring(@s,number,charindex(',',@s+',',number)-number))
from master..spt_values
where type='p' and number<=len(@s+'a') and charindex(',',','+@s,number)=number)
end
go
select
[lvl1],
[lvl2],
[lvl3],
[lvl4],
[lvl]=dbo.UF_minget(ltrim([lvl1])+','+ltrim([lvl2])+','+ltrim([lvl3])+','+ltrim([lvl4]))
from #T
/*
lvl1 lvl2 lvl3 lvl4 lvl
----------- ----------- ----------- ----------- -----------
4 3 4 1 1
3 2 2 1 1
2 2 3 4 2
4 4 3 4 3
3 1 2 2 1

*/

--方法(五)

-->Title:Generating test data
-->Author:wufeng4552
-->Date :2009-10-16 09:58:16
if not object_id('Tempdb..#t') is null
drop table #t
Go
Create table #t([lvl1] int,[lvl2] int,[lvl3] int,[lvl4] int,[lvl] int)
Insert #t
select 4,3,4,1,null union all
select 3,2,2,1,null union all
select 2,2,3,4,null union all
select 4,4,3,4,null union all
select 3,1,2,2,null
Go
select [lvl1],
[lvl2],
[lvl3],
[lvl4],
[lvl]=(select min([lvl1])
from (select [lvl1]
union all select [lvl2]
union all select [lvl3]
union all select [lvl4])T)
from #t
/*
lvl1 lvl2 lvl3 lvl4 lvl
----------- ----------- ----------- ----------- -----------
4 3 4 1 1
3 2 2 1 1
2 2 3 4 2
4 4 3 4 3
3 1 2 2 1

(5 個資料列受到影響)
*/
--方法六 作者:josy (樹哥)

-->测试数据
if object_id('[tb]') is not null drop table [tb]
go
create table [tb]([lvl1] int,[lvl2] int,[lvl3] int,[lvl4] int,[lvl] int)
insert [tb]
select 4,3,4,1,null union all
select 3,2,2,1,null union all
select 2,2,3,4,null union all
select 4,4,3,4,null union all
select 3,1,2,2,null
go

-->函数：返回两个数中值较小的数
if object_id('F_GetMin')is not null drop function F_GetMin
go
CREATE FUNCTION F_GetMin
(
@arg1 AS int,
@arg2 AS int
)
RETURNS int
AS
BEGIN
RETURN CASE
WHEN @arg1<=@arg2 THEN @arg1
WHEN @arg1>@arg2 THEN @arg2
ELSE NULL
END
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