Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru> writes:
> ERROR: RANGE PRECEDING is only supported with UNBOUNDED
> Is there some principle problem in implementing such kind of window?
There was such code in the original windowagg patch and it got rejected
as being too broken. Please consult the archives.
> Certainly it assumes that window is ordered by key and the key type
> supports subtraction, so "text" can not be used here.
IIRC, the sticking point was defining a reasonably datatype-independent
(i.e. extensible) notion of distance.
regards, tom lane