Alex Shulgin <alex.shul...@gmail.com> writes: > On Sun, Apr 3, 2016 at 7:18 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: >> Well, we have to do *something* with the last (possibly only) value. >> Neither "include always" nor "omit always" seem sane to me. What other >> decision rule do you want there?
> Well, what implies that the last value is somehow special? I would think > we should just do with it whatever we do with the rest of the candidate > MCVs. Sure, but both of the proposed decision rules break down when there are no values after the one under consideration. We need to do something sane there. > For "the only value" case: we cannot build a histogram out of a single > value, so omitting it from MCVs is not a good strategy, ISTM. > From my point of view that amounts to "include always". If there is only one value, it will have 100% of the samples, so it would get included under just about any decision rule (other than "more than 100% of this value plus following values"). I don't think making sure this case works is sufficient to get us to a reasonable rule --- it's a necessary case, but not a sufficient case. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers