self join revisited

How hard would it be to teach planer to optimize self join?

While this query which demonstrates it is not that common

SELECT count(*)
FROM
big_table a
INNER JOIN big_table b ON a.id = b.id;

This type of query (self joining large table) is very common
(at least in our environment because of heavy usage of views).

It would be great if Postgres could rewrite this query

SELECT bt1.id, bt1.total, sq.id, sq.total
FROM
big_table bt1
INNER JOIN small_table st1 on st1.big_id = bt1.id
INNER JOIN
(
SELECT bt2.id, st2.total
FROM
big_table bt2
INNER JOIN small_table st2 on st2.big_id = bt2.id
WHERE
st2.total > 100
) sq ON sq.id = bt1.id
WHERE
st1.total<200

like this

SELECT bt1.id, bt1.total, bt1.id, st2.total
FROM
big_table bt1
INNER JOIN small_table st1 on st1.big_id = bt1.id
INNER JOIN small_table st2 on st2.big_id = bt1.id AND st2.total > 100
WHERE
st1.total<200

Regards,
Rikard