"select c1, method(c2) group by c1" returns all values of c2 for c1

Good afternoon,

Is there a method to retrieve the following results:

T1(c1 int, c2 varchar(128) )
---------------------------------


(1, val1);
(1, val2);
(1, val3);
(2, val1);
(3, val5);
(3, val6);

select c1, method(c2)
group by c1

returns:
============
1,   "val1, val2, val3"
2,   "val1"
3,   "val5, val6"


Thanks a lot!

--
Lu Ying