一个SQL语句的写法,求思路,谢谢

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

-- Author  :fredrickhu(小F，向高手学习)

-- Date    :2010-06-01 22:40:57

-- Version:

--      Microsoft SQL Server 2005 - 9.00.4035.00 (Intel X86) 

--	Nov 24 2008 13:01:59 

--	Copyright (c) 1988-2005 Microsoft Corporation

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

--

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

--> 测试数据：[tb]

if object_id('[tb]') is not null drop table [tb]

go 

create table [tb]([col1] varchar(4),[col2] varchar(3),[col3] varchar(6))

insert [tb]

select '小明','2班','品德好' union all

select '小明','2班','身体差' union all

select '小红','2班','品德好' union all

select '小绿','1班','身体好'

--------------开始查询--------------------------

select

 col1,col2, [col3]=stuff((select '+'+[col3] from tb t where col1=tb.col1 for xml path('')), 1, 1, '') 

from

 tb 

group by

 col1,col2 

----------------结果----------------------------

/* col1 col2 col3

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

小红   2班   品德好

小绿   1班   身体好

小明   2班   品德好+身体差



(3 行受影响)



*/

合并列值 

--*******************************************************************************************

表结构，数据如下： 

id    value 

----- ------ 

1    aa 

1    bb 

2    aaa 

2    bbb 

2    ccc 



需要得到结果： 

id    values 

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

1      aa,bb 

2      aaa,bbb,ccc 

即：group by id, 求 value 的和（字符串相加） 



1. 旧的解决方法(在sql server 2000中只能用函数解决。) 

--=============================================================================

create table tb(id int, value varchar(10)) 

insert into tb values(1, 'aa') 

insert into tb values(1, 'bb') 

insert into tb values(2, 'aaa') 

insert into tb values(2, 'bbb') 

insert into tb values(2, 'ccc') 

go 

--1. 创建处理函数 

CREATE FUNCTION dbo.f_strUnite(@id int) 

RETURNS varchar(8000) 

AS 

BEGIN 

    DECLARE @str varchar(8000) 

    SET @str = '' 

    SELECT @str = @str + ',' + value FROM tb WHERE id=@id 

    RETURN STUFF(@str, 1, 1, '') 

END 

GO 

-- 调用函数 

SELECt id, value = dbo.f_strUnite(id) FROM tb GROUP BY id 

drop table tb 

drop function dbo.f_strUnite 

go

/* 

id          value      

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

1          aa,bb 

2          aaa,bbb,ccc 

（所影响的行数为 2 行） 

*/ 

--===================================================================================

2. 新的解决方法(在sql server 2005中用OUTER APPLY等解决。) 

create table tb(id int, value varchar(10)) 

insert into tb values(1, 'aa') 

insert into tb values(1, 'bb') 

insert into tb values(2, 'aaa') 

insert into tb values(2, 'bbb') 

insert into tb values(2, 'ccc') 

go 

-- 查询处理 

SELECT * FROM(SELECT DISTINCT id FROM tb)A OUTER APPLY( 

        SELECT [values]= STUFF(REPLACE(REPLACE( 

            ( 

                SELECT value FROM tb N 

                WHERE id = A.id 

                FOR XML AUTO 

            ), ' <N value="', ','), '"/>', ''), 1, 1, '') 

)N 

drop table tb 



/* 

id          values 

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

1          aa,bb 

2          aaa,bbb,ccc 



(2 行受影响) 

*/ 



--SQL2005中的方法2 

create table tb(id int, value varchar(10)) 

insert into tb values(1, 'aa') 

insert into tb values(1, 'bb') 

insert into tb values(2, 'aaa') 

insert into tb values(2, 'bbb') 

insert into tb values(2, 'ccc') 

go 



select id, [values]=stuff((select ','+[value] from tb t where id=tb.id for xml path('')), 1, 1, '') 

from tb 

group by id 



/* 

id          values 

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

1          aa,bb 

2          aaa,bbb,ccc 



(2 row(s) affected) 



*/ 



drop table tb 

--合并分拆表

/******************************************************************************************************************************************************

合并分拆表数据



整理人：中国风(Roy)



日期:2008.06.06

******************************************************************************************************************************************************/



--> --> (Roy)生成測試數據

 

if not object_id('Tab') is null

    drop table Tab

Go

Create table Tab([Col1] int,[Col2] nvarchar(1))

Insert Tab

select 1,N'a' union all

select 1,N'b' union all

select 1,N'c' union all

select 2,N'd' union all

select 2,N'e' union all

select 3,N'f'

Go



合并表:



SQL2000用函数:



go

if object_id('F_Str') is not null

    drop function F_Str

go

create function F_Str(@Col1 int)

returns nvarchar(100)

as

begin

    declare @S nvarchar(100)

    select @S=isnull(@S+',','')+Col2 from Tab where Col1=@Col1

    return @S

end

go

Select distinct Col1,Col2=dbo.F_Str(Col1) from Tab



go



SQL2005用XML:



方法1:



select 

    a.Col1,Col2=stuff(b.Col2.value('/R[1]','nvarchar(max)'),1,1,'')

from 

    (select distinct COl1 from Tab) a

Cross apply

    (select COl2=(select N','+Col2 from Tab where Col1=a.COl1 For XML PATH(''), ROOT('R'), TYPE))b



方法2:



select 

    a.Col1,COl2=replace(b.Col2.value('/Tab[1]','nvarchar(max)'),char(44)+char(32),char(44))

from 

    (select distinct COl1 from Tab) a

cross apply

    (select Col2=(select COl2 from Tab  where COl1=a.COl1 FOR XML AUTO, TYPE)

                .query('<Tab>

                {for $i in /Tab[position()<last()]/@COl2 return concat(string($i),",")}

                {concat("",string(/Tab[last()]/@COl2))}

                </Tab>')

                )b



SQL05用CTE:



;with roy as(select Col1,Col2,row=row_number()over(partition by COl1 order by COl1) from Tab)

,Roy2 as

(select COl1,cast(COl2 as nvarchar(100))COl2,row from Roy where row=1 

union all 

select a.Col1,cast(b.COl2+','+a.COl2 as nvarchar(100)),a.row from Roy a join Roy2 b on a.COl1=b.COl1 and a.row=b.row+1)

select Col1,Col2 from Roy2 a where row=(select max(row) from roy where Col1=a.COl1) order by Col1 option (MAXRECURSION 0)





生成结果:

/*

Col1        COl2

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

1           a,b,c

2           d,e

3           f



(3 行受影响)

*/

create function getstr(@col1 varchar(20))

returns varchar(100)

as

begin

       declare @sql varchar(100)

       select @sql=isnull(@sql+'+','')+col3 from 表名 where col1=@col1

       return @sql

end

go



--调用：

select distinct col1,col2,dbo.getstr(col1) from 表名