On Jan19, 2011, at 23:44 , Nathan Boley wrote: > If you think about it, it's a bit ridiculous to look at the whole table > *just* to "estimate" ndistinct - if we go that far why dont we just > store the full distribution and be done with it?
The crucial point that you're missing here is that ndistinct provides an estimate even if you *don't* have a specific value to search for at hand. This is way more common than you may think, it e.g. happens every you time PREPARE are statement with parameters. Even knowing the full distribution has no advantage in this case - the best you could do is to average the individual probabilities which gives ... well, 1/ndistinct. best regards, Florian Pflug -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
