create table aa(id,str)
   insert aa values (1,'a,d,c,f')
   insert aa values (2,'f,a')

declare  @aa table(id int ,str varchar(20))
   insert @aa values (1,'a,d,c,f')
   insert @aa values (2,'f,a')

;
WITH T 
AS
(   
    SELECT top 26 ROW_NUMBER() OVER (ORDER BY ID) AS n
   FROM SYS.SYSOBJECTS
),
T2
AS
(
    SELECT str,CHAR(64+N) AS M,N
    FROM @aa JOIN T
    ON CHARINDEX(CHAR(64+N),str) > 0
)
SELECT 
    str,
    replace(
    (SELECT M as [data()]  FROM T2 WHERE str = T3.str ORDER BY N FOR XML PATH('')
    ),' ',',') AS newstr
FROM @aa T3


/*
str                  newstr
-------------------- ------------
a,d,c,f              A,C,D,F
f,a                  A,F
*/

------解决方案--------------------
探讨

SQL codecreatetable aa(id,str)insert aavalues (1,'a,d,c,f')insert aavalues (2,'f,a')

 期望结果
 id       str
 1        a,c,d,f
 2        a,f


------解决方案--------------------
SQL code
declare  @aa table(id int ,str varchar(20))
   insert @aa values (1,'a,d,c,f')
   insert @aa values (2,'f,a')

;with t as
(
    select [az]=char(number) 
    from master..spt_values 
    where type='p' and number between 97 and 122
),t1 as
(
    select a.id,t.az 
    from t,@aa a 
    where charindex(az,str)>0
)
select id,stuff((select ','+az from t1 where id=a.id order by az for xml path('')),1,1,'') newstr 
from t1 a 
group by id
/*
id          newstr
----------- ----------------
1           a,c,d,f
2           a,f
*/

------解决方案--------------------

SQL code
 create table aa(id int ,str varchar(1000))
   insert aa values (1,'a,d,c,f')
   insert aa values (2,'f,a')
    insert aa values(3,'aaaa,呵呵,哈哈,123')
go
create function f_test(@str varchar(8000))
returns varchar(8000)
as
begin
    declare @ret varchar(8000)
    set @ret=''
    declare @s xml
    select @s=cast('<item><S>'+replace(@str,',','</S></item><item><S>')+'</S></item>' as xml)
    declare @tb table(str varchar(8000))
    select @ret=@ret+','+str from (select A.x.value('S[1]','varchar(8000)')  as str
        from @s.nodes('//item')AS A(x))t order by str
    return right(@ret,len(@ret)-1)
end
go
select *,dbo.f_test(str) from aa
go
drop function f_test
drop table aa 

/*
1    a,d,c,f                    a,c,d,f
2    f,a                        a,f
3    aaaa,呵呵,哈哈,123        123,aaaa,哈哈,呵呵
*/