postgres=# select * from t order by id;
  id  | pid  | rate
------+------+------
 1000 |    0 |    8
 1001 |    0 |    9
 1002 |    0 |   40
 2000 | 1002 |   24
 2001 | 1002 |    4
 2002 | 1002 |   12
 3000 | 2002 |    7
 3001 | 2002 |    2
(8 rows)