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Re: review: More frame options in window functions

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Hitoshi Harada <umi(dot)tanuki(at)gmail(dot)com>
Cc: Erik Rijkers <er(at)xs4all(dot)nl>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: review: More frame options in window functions
Date: 2010-01-19 01:24:33
Message-ID: 20727.1263864273@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Hitoshi Harada <umi(dot)tanuki(at)gmail(dot)com> writes:
> 2010/1/19 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)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

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