From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, Vik Fearing <vik(at)postgresfriends(dot)org>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: ANY_VALUE aggregate |
Date: | 2022-12-05 18:06:53 |
Message-ID: | CA+TgmoaKUOFGLDFeOOmxR7Z1KbLZ5fYWEMoXvx0hGAY4Op8OnQ@mail.gmail.com |
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On Mon, Dec 5, 2022 at 1:04 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> "David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> > Can we please add "first_value" and "last_value" if we are going to add
> > "some_random_value" to our library of aggregates?
>
> First and last according to what ordering? We have those in the
> window-aggregate case, and I don't think we want to encourage people
> to believe that "first" and "last" are meaningful otherwise.
>
> ANY_VALUE at least makes it clear that you're getting an unspecified
> one of the inputs.
I have personally implemented first_value() and last_value() in the
past in cases where I had guaranteed the ordering myself, or didn't
care what ordering was used. I think they're perfectly sensible. But
if we don't add them to core, at least they're easy to add in
user-space.
--
Robert Haas
EDB: http://www.enterprisedb.com
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