/*

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