> I think the real question is: what other kinds of correlation might > people be interested in representing?
Yes, or to phrase that another way: What kinds of queries are being poorly optimized now and why? I suspect that a lot of the correlations people care about are extreme. For example, it's fairly common for me to have a table where column B is only used at all for certain values of column A. Like, atm_machine_id is usually or always NULL unless transaction_type is ATM, or something. So a clause of the form transaction_type = 'ATM' and atm_machine_id < 10000 looks more selective than it really is (because the first half is redundant). The other half of this is that bad selectivity estimates only matter if they're bad enough to change the plan, and I'm not sure whether cases like this are actually a problem in practice. ...Robert -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
