Dne 13.12.2010 16:34, Tom Lane napsal(a): > Tomas Vondra <t...@fuzzy.cz> writes: >> Well, until this point we've discussed failure cases involving 'AND' >> conditions. What about 'OR' conditions? I think the current optimizer >> computes the selectivity as 's1+s2 - s1*s2' (at least that's what I >> found in backend/optimizer/path/clausesel.c:630). > > If you can solve the AND case, the OR case falls out of that. Just > replace s1*s2 with a more accurate AND calculation.
Oh yeah, now I see - it's just the usual equation P(A or B) = P(A) + P(B) - P(A and B) and we're estimating "P(A and B)" as P(A)*P(B). regards Tomas -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
