Re: BUG #14676: neqsel is NULL dumb

marko(at)joh(dot)to writes:
> This seems to be because neqsel() doesn't take at all into account that both
> operators will exclude NULL rows, and does a simple 1.0 - eqsel().

Yeah, that's clearly broken. A localized fix would be to re-fetch the
nullfrac statistic and subtract it off, but that seems pretty inefficient.
I'd be inclined to refactor things so that eqsel() and neqsel() call a
common routine that takes a "bool negate" argument, about like the way the
patternsel() functions work, and then the common routine could handle
the nullfrac correctly for both cases.

Hmm ... actually, I think patternsel() is broken for this case too ---
it has the information to do the right thing, but it doesn't look like
it actually is doing it:
return negate ? (1.0 - result) : result;
should be more like
return negate ? (1.0 - result - nullfrac) : result;

neqjoinsel has a similar issue, and I'm not sure what else.

regards, tom lane