=?ISO-8859-2?Q?pasman_pasma=F1ski?= <pasman(dot)p(at)gmail(dot)com> writes:
> My english is not perfect, by accumulative i think about monotonically
> increasing function.
Oh, I see how that would work. I can't get real excited about it
though. The use-case seems a bit narrow, and the amount of complexity
added to the btree search mechanism (thereby slowing down all btree
searches) would be significant. Furthermore, unless f() is pretty cheap
to evaluate, you'd end up preferring an index on f(x) anyway, because
that can be searched without any new evaluations of f().
regards, tom lane