Re: Clarify note about DISTINCT and ORDER BY in aggregates

On Thu, Dec 8, 2022 at 5:31 AM Vik Fearing <vik(at)postgresfriends(dot)org> wrote:

> The current docs can be read as using DISTINCT in an aggregate
> (count(distinct col)) and ORDER BY (array_agg(col ORDER BY col)) are
> both extensions to the standard.
>
> The actual truth is that our extension to the standard is to allow both
> at the same time.
>
> Attached is a trivial patch to make that more clear. I don't know if
> pgindent works on the docs so I made this so as to show what is
> changing. I can submit a properly formatted patch, or let the eventual
> committer make that change if necessary.
>

From the other thread this still is off compared to reality, which you
described as:

"The SQL Standard defines whether DISTINCT or ORDER BY are accepted on a
per-aggregate basis. It is a PostgreSQL extension that any aggregate can
specify these clauses."

The fact that no SQL Standard aggregate happens to specify both DISTINCT
and ORDER BY at the same time is a detail we don't need to cover. We
aren't documenting the per-aggregate variances.

David J.