Hitoshi Harada <umi.tanuki@gmail.com> writes:
> 2010/1/19 Tom Lane <tgl@sss.pgh.pa.us>:
>> AFAICS that doesn't mean it can't be the
>> canonicalized form of the sort key. �If a column is dropped out of the
>> canonical sort key then it's simply redundant, and hence not relevant to
>> determining the range.
> Yeah, that's my point, too. The planner has to distinguish "four" from
> sort pathkeys and to teach the executor the simple information which
> column should be used to determine frame. I was bit wrong because some
> of current executor code isn't like it, like using ordNumCols == 0 to
> know whether partition equals to frame, though....
BTW, watch out for the possibility that the canonicalized key is empty.
This isn't an error case --- what it means is that the planner has
proven that all the rows have equal sort key values, so there's no
need to compare anything.
regards, tom lane