Column values separated by ,

Question

Suppose say I have table TAB1 with the following data :
COL1 COL2
1 A
1 B
1 C
2 M
2 N
2 O
2 P
2 Q
3 S
3 T
How would I retrieve the data in the following format ?
1 A,B,C
2 M,N,O,P,Q
3 S,T

Answer 1

Hi Laurent Schneider.
That a good solution.
I researched that.
SQL> select version from v$instance;
VERSION
10.2.0.1.0
SQL> create table IDTable(ID,Val) as
  2  select 10,'abc' from dual union all
  3  select 10,'abc' from dual union all
  4  select 10,'def' from dual union all
  5  select 10,'def' from dual union all
  6  select 20,'ghi' from dual union all
  7  select 20,'jkl' from dual union all
  8  select 20,'mno' from dual union all
  9  select 20,'mno' from dual;
SQL> col enames for a40
SQL> select ID,wmsys.wm_concat(Val) as enames
  2    from IDTable
  3  group by ID
  4  order by ID;
ID  ENAMES
10  abc,abc,def,def
20  ghi,jkl,mno,mno
SQL> select ID,wmsys.wm_concat(distinct Val) as enames
  2    from IDTable
  3  group by ID
  4  order by ID;
ID  ENAMES
10  abc,def
20  ghi,jkl,mno
SQL> select ID,wmsys.wm_concat(Val order by Val) as enames
  2    from IDTable
  3  group by ID
  4  order by ID;
select ID,wmsys.wm_concat(Val order by Val) as enames
ORA-00907:
SQL> select ID,Val,wmsys.wm_concat(Val) over(partition by ID) as enames
  2    from IDTable
  3  order by ID;
ID  VAL  ENAMES
10  abc  abc,abc,def,def
10  abc  abc,abc,def,def
10  def  abc,abc,def,def
10  def  abc,abc,def,def
20  ghi  ghi,jkl,mno,mno
20  jkl  ghi,jkl,mno,mno
20  mno  ghi,jkl,mno,mno
20  mno  ghi,jkl,mno,mno
SQL> select ID,Val,wmsys.wm_concat(Val) over(order by ID,Val) as enames
  2    from IDTable
  3  order by ID;
ID  VAL  ENAMES
10  abc  abc,abc
10  abc  abc,abc
10  def  abc,abc,def,def
10  def  abc,abc,def,def
20  ghi  abc,abc,def,def,ghi
20  jkl  abc,abc,def,def,ghi,jkl
20  mno  abc,abc,def,def,ghi,jkl,mno,mno
20  mno  abc,abc,def,def,ghi,jkl,mno,mno