alter table tabla add (no number);
update tabla set no = rownum;
declare
  cursor cur1 is select * from tabla;
  cursor cur2 is select * from tabla;
begin
  for e in cur1
  loop
    for f in cur2
    loop
      if (e.cim_id = f.cim_id) and (e.cat_id = f.cat_id) and (e.no <> f.no)
      then
        delete from tabla where (cim_id = e.cim_id) and (cat_id = e.cat_id) and (no = e.no);
      end if;
    end loop;
  end loop;
end;
/
alter table tabla drop column no;