| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Nico Williams <nico(at)cryptonector(dot)com> |
| Cc: | Merlin Moncure <mmoncure(at)gmail(dot)com>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, Vik Fearing <vik(at)postgresfriends(dot)org>, Matheus Alcantara <matheusssilv97(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Peter Eisentraut <peter(at)eisentraut(dot)org> |
| Subject: | Re: Proposal: QUALIFY clause |
| Date: | 2025-07-22 05:14:20 |
| Message-ID: | 881159.1753161260@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Nico Williams <nico(at)cryptonector(dot)com> writes:
> On Mon, Jul 21, 2025 at 09:43:15PM -0600, Merlin Moncure wrote:
>> Hm, HAVING requires to apply 'group by' which windows functions do not
>> require (unlike aggregates).
> Pavel's point is precisely to allow HAVING w/o a GROUP BY when there are
> window functions since window functions are "+/-" ("more or less")
> aggregate functions. That makes sense to me.
No, it's really quite wrong. Aggregate functions are not equivalent
to window functions: if you have both in a query, they execute in
separate passes, with the window functions operating on the grouped
rows output by the aggregation step (and then filtered by HAVING,
if any).
If we're going to support this, it does need to be its own clause.
regards, tom lane
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