On Dec17, 2010, at 23:12 , Tomas Vondra wrote: > Well, not really - I haven't done any experiments with it. For two > columns selectivity equation is > > (dist(A) * sel(A) + dist(B) * sel(B)) / (2 * dist(A,B)) > > where A and B are columns, dist(X) is number of distinct values in > column X and sel(X) is selectivity of column X.
Huh? This is the selectivity estimate for "A = x AND B = y"? Surely, if A and B are independent, the formula must reduce to sel(A) * sel(B), and I cannot see how that'd work with the formula above. 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
