Andrea Arcangeli <andrea@xxxxxxxxxxxx> writes: > If you don't know the data, I think it's a bug that LIKE is assumed to > have a selectivity above 50%. Extrapolating from the observation that the heuristics don't work well on your data to the conclusion that they don't work for anybody is not good logic. Replacing that code with a flat 50% is not going to happen (or if it does, I'll be sure to send the mob of unhappy users waving torches and pitchforks to your door not mine ;-)). I did just think of something we could improve though. The pattern selectivity code doesn't make any use of the statistics about "most common values". For a constant pattern, we could actually apply the pattern test with each common value and derive answers that are exact for the portion of the population represented by the most-common-values list. If the MCV list covers a large fraction of the population then this would be a big leg up in accuracy. Dunno if that applies to your particular case or not, but it seems worth doing ... regards, tom lane
