Concat result of a sub-select in a single field

Question

How can I concat all registers of a sub-select in a single field.
like:
SELECT DATE_MARK
FROM TABLE_A
WHERE COD = '123'
RESULT:
200601
200605
200607
200507
How can I put that result in a single field? like this:
'200601 200605 200607 200507'
Thanks.

Answer 1

In a little different approach ->
satyaki>
satyaki>select * from v$version;
BANNER
Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - Prod
PL/SQL Release 10.2.0.3.0 - Production
CORE    10.2.0.3.0      Production
TNS for 32-bit Windows: Version 10.2.0.3.0 - Production
NLSRTL Version 10.2.0.3.0 - Production
Elapsed: 00:00:00.01
satyaki>
satyaki>
satyaki>drop type pipe_rec;
Type dropped.
Elapsed: 00:00:05.47
satyaki>
satyaki>
satyaki>create or replace type pipe_obj as object
  2    (
  3      dno       number(5),
  4      buff      clob
  5    );
  6  /
Type created.
Elapsed: 00:00:00.24
satyaki>
satyaki>create or replace type pipe_rec as table of pipe_obj;
  2  /
Type created.
Elapsed: 00:00:00.17
satyaki>
satyaki>
satyaki>create or replace function pivot_horizon(d_no  in number)
  2  return pipe_rec
  3  pipelined is
  4    cursor c1
  5    is
  6      select ename
  7      from emp
  8      where deptno = d_no;
  9     
10   r1 c1%rowtype;
11  
12   str clob;
13  begin
14    str:= '';
15    for r1 in c1
16    loop
17      str := str||' '||r1.ename;
18    end loop;
19      pipe row(pipe_obj(d_no,trim(str)));
20    return;
21  end;
22  /
Function created.
Elapsed: 00:00:00.18
satyaki>
satyaki>
satyaki>
satyaki>
satyaki>select *
  2  from table(cast(pivot_horizon(10) as pipe_rec));
       DNO BUFF
        10 SOURAV  CLARK KING
Elapsed: 00:00:00.11
satyaki>
satyaki>
satyaki>Regards.
Satyaki De.