postgres=# 
WITH RECURSIVE cte(id, pid, rate) AS
(SELECT id,
        pid,
        rate
  FROM  t a
  UNION ALL
  SELECT cte.id,
         b.pid,
         b.rate * cte.rate / 100
  FROM t b
  INNER JOIN cte ON b.id = cte.pid
)
SELECT id, rate FROM cte WHERE pid = 0 ORDER BY id;

  id  | rate
------+------
 1000 |    8
 1001 |    9
 1002 |   40
 2000 |   24
 2001 |    4
 2002 |   12
 3000 |    7
 3001 |    2
(8 rows)