create table subdiv (ID integer, PARENT integer);

insert into AAA (ID, PARENT) values ( 1 , NULL);
insert into AAA (ID, PARENT) values ( 2 ,  1 );
insert into AAA (ID, PARENT) values ( 3 ,  1 );
insert into AAA (ID, PARENT) values ( 4 ,  2 );
insert into AAA (ID, PARENT) values ( 5 ,  3 );

create function rec(aid integer) returns SETOF integer as $$
declare
 r integer;
begin
 for r in select id from aaa where parent=aid loop
  IF FOUND THEN
   perform rec(r);
  end if;
  return next r;
 end loop;
end
$$
language 'plpgsql';

SELECT * FROM rec( 1 );
 rec
-----
 4 
 2 
 5 
 3 
( 4  rows)

select * from rec( 1 );
 rec
-----
    2 
    3 
( 2  rows)

CREATE OR REPLACE FUNCTION "rec" (_id integer, out _name varchar) RETURNS varchar AS
$body$
DECLARE
    nm varchar;  
    self_id varchar;
    r integer;
BEGIN
    self_id:='';
    FOR r IN SELECT id FROM aaa WHERE parent = _id LOOP  

      self_id = r || ',' || self_id; 
     SELECT rec(r) INTO nm;
      self_id = nm || '' || self_id; 

   END LOOP;
    _name =  self_id;
    RETURN;
END;
$body$
LANGUAGE 'plpgsql' VOLATILE CALLED ON NULL INPUT SECURITY INVOKER;

web=# select * from aaa;
 id | parent
----+--------
   1  |
   2  |       1 
   3  |       1 
   4  |       2 
   5  |       3 
   6  |       1 
   7  |       6 
   8  |       6 
   9  |       6 
  10  |       7 
( 10  rows)

web=# select rec( 1 );
         rec
---------------------
  9 , 8 , 10 , 7 , 6 , 5 , 3 , 4 , 2 ,
( 1  запись)