query: last N price for each product? - Mailing list pgsql-sql

Dear SQL masters,

The query for "latest price for each product" goes like this (which I
can grasp quite easily):
SELECT * FROM price p1WHERE ctime=(SELECT MAX(ctime) FROM price p2 WHERE p1.product_id=p2.product_id)

or:
SELECT * FROM price p1WHERE NOT EXISTS (SELECT * FROM price p2 WHERE
p1.product_id=p2.product_id AND p1.ctime < p2.ctime)

but how do yo query for "latest 3 prices for each product"? The
"price" table contains current price as well as price histories.

Regards,
dave