合并字符串.txt

SQL语言常用的一些命令各代码

tab1
c1 c2
--- ---
001 a
001 b
001 c
002 a
002 b
003 b
...
现在想实现如下的格式
c1 c2
--- ---
001 a,b,c
002 a,b
003 b
请问如何用SQL解决,不胜感激

/*解答：*/
create table tab1(c1 varchar(5),c2 char(1))
insert into tab1 select '0001','a'
union all        select '0001','b'
union all        select '0001','c'
union all        select '0002','a'
union all        select '0002','b'
union all        select '0003','b'

declare @A table(a int identity(1,1),c1 varchar(5),c2 char(1))
insert into @A(c1,c2)
select c1,c2 from tab1 order by c1 desc
declare @anser table (c1 varchar(5),c2 varchar(10))
declare @b varchar(5),@c varchar(10),@d int
select @b=(select min(c1) from tab1)
while @b<=(select max(c1) from tab1)
begin
select @d=(select min(a) from  (select a from @A where c1=@b) X)
select @c=''        
          while @d<=(select max(a) from  (select a from @A where c1=@b) X)
            begin
            select @c=@c+(select c2 from @A where c1=@b and a=@d)+','
            select @d=(select min(a) from (select a from @A where c1=@b and a>@d) X)
            end
 insert into @anser select @b,left(@c,len(@c)-1)
 select @b=(select min(c1) from tab1 where c1>@b)
end
select * from @anser