| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
| Cc: | Sky Lendar <skylendar(at)gmail(dot)com>, pgsql-general(at)lists(dot)postgresql(dot)org |
| Subject: | Re: sorting problem with distinct on() |
| Date: | 2023-05-05 14:26:18 |
| Message-ID: | 3585863.1683296778@sss.pgh.pa.us |
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| Lists: | pgsql-general |
"David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> On Fri, May 5, 2023 at 6:55 AM Sky Lendar <skylendar(at)gmail(dot)com> wrote:
>> Notice that 12 is missing in the list.
> Since your DISTINCT ON *subquery* doesn't specify an ordering which of
> those two are chosen as the representative record for M31 is
> non-determinstic.
> If you want to ensure the lowest valued nb is chosen you need to sort the
> *subquery*.
The "weather_reports" example here might help clarify this for you:
https://www.postgresql.org/docs/current/sql-select.html
regards, tom lane
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