SQL SERVER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
怎麼寫代碼 去比較lvl1、lvl2、lvl3、lvl4 對應每行的值，取其中最小的，將其值添加到lvl列裡
運行結果應該是
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 梁愛蘭
--  Comment: 小梁 愛 蘭兒
--  Date   : 2009-10-16 09:57:38
-------------------------------------

--> 產生測試資料: @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查詢如下:

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 行受影響)

*/
--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

-->查詢
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 行受影響)
**/

--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)
*/

 

轉載：http://blog.csdn.net/navy887/archive/2009/10/16/4682433.aspx