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