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Re: TODO items for 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: pgsql-hackers(at)postgresql(dot)org
Subject: Re: TODO items for window functions
Date: 2008-12-29 16:44:30
Message-ID: 8706.1230569070@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
"Hitoshi Harada" <umi(dot)tanuki(at)gmail(dot)com> writes:
> 2008/12/29 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
>> * Support creation of user-defined window functions.  I think this is
>> a "must have" for 8.4 --- we are not in the habit of building
>> nonextensible basic features.  It doesn't seem that hard either.

> The reason I and people decided window functions are not able to be
> defined by user is whether Window functions API is ready for exposure.

Well, it seems about as stable as any other bit of new backend code ;-).
We never promise that backend-internal APIs will not change across
versions.

> My only concern is for plpgsql. For c functions we can define user
> functions but what about other pls?

I'm not concerned about making this stuff available at the PL level
(at least not yet).  C-level capability will be enough to satisfy
my concern for 8.4.

> And surveying sgml docs, I found this is not correct.

> http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/select.sgml?r1=1.112&r2=1.113

> +     default framing behavior, which is equivalent to the framing clause
> +     <literal>ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW</>.

> the default frame with ORDER BY clause is RANGE BETWEEN UNBOUNDED
> PRECEDING AND CURRENT ROW, as aggregates perform rows peer to the
> current row.

What is the difference?  AFAICS the RANGE and ROWS keywords ought to be
equivalent if you are not specifying "expression PRECEDING" or
"expression FOLLOWING".

			regards, tom lane

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