Martijn van Oosterhout <[EMAIL PROTECTED]> writes: > I think you need to go a step back: how are you going to use this data?
The fundamental issue as the planner sees it is not having to assume independence of WHERE clauses. For instance, given WHERE a < 5 AND b > 10 our current approach is to estimate the fraction of rows with a < 5 (using stats for a), likewise estimate the fraction with b > 10 (using stats for b), and then multiply these fractions together. This is correct if a and b are independent, but can be very bad if they aren't. So if we had joint statistics on a and b, we'd want to somehow match that up to clauses for a and b and properly derive the joint probability. (I'm not certain of how to do that efficiently, even if we had the right stats :-() regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers