| From: | Vik Fearing <vik(at)postgresfriends(dot)org> |
|---|---|
| To: | David Rowley <dgrowleyml(at)gmail(dot)com>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Erwin Brandstetter <brsaweda(at)gmail(dot)com> |
| Subject: | Re: Allow WindowFuncs prosupport function to use more optimal WindowClause options |
| Date: | 2022-10-12 03:33:33 |
| Message-ID: | 2c12c34b-8a71-888f-a6e2-757a03ba56f3@postgresfriends.org |
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| Lists: | pgsql-hackers |
On 10/12/22 04:40, David Rowley wrote:
> I've not really done any analysis into which other window functions
> can use this optimisation. The attached only adds support to
> row_number()'s support function and only converts exactly "RANGE
> UNBOUNDED PRECEDING AND CURRENT ROW" into "ROW UNBOUNDED PRECEDING AND
> CURRENT ROW". That might need to be relaxed a little, but I've done
> no analysis to find that out.
Per spec, the ROW_NUMBER() window function is not even allowed to have a
frame specified.
b) The window framing clause of WDX shall not be present.
Also, the specification for ROW_NUMBER() is:
f) ROW_NUMBER() OVER WNS is equivalent to the <window function>:
COUNT (*) OVER (WNS1 ROWS UNBOUNDED PRECEDING)
So I don't think we need to test for anything at all and can
indiscriminately add or replace the frame with ROWS UNBOUNDED PRECEDING.
--
Vik Fearing
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