How to get a similar value in Oracle

Question

I have a table of two columns

Col1  Col2
A        1
A        2
A        3
B        1
B        2
B        3

Output I need is like this

Answer 1

with s (Col1, Col2) as (
select 'A', 1 from dual union all
select 'A', 2 from dual union all
select 'A', 3 from dual union all
select 'B', 1 from dual union all
select 'B', 2 from dual union all
select 'B', 3 from dual)
select col1, ltrim(sys_connect_by_path(col2, ','), ',') path
from s
start with col2 = 1
connect by prior col2 = col2 - 1 and prior col1 = col1;

C PATH
- ----------
A 1
A 1,2
A 1,2,3
B 1
B 1,2
B 1,2,3

6 rows selected.