Re: Document aggregate functions better w.r.t. ORDER BY

On Tue, Dec 13, 2022 at 07:38:15PM -0700, David G. Johnston wrote:
> All,
>
> The recent discussion surrounding aggregates and ORDER BY moved me to look over
> our existing documentation, especially now that we've reworked the function
> tables, to see what improvements can be had by simply documenting those
> functions where ORDER BY may change the user-visible output.  I skipped range
> aggregates for the moment but handled the others on the aggregates page (not
> window functions).  This includes the float types for sum and avg.
>
> I added a note just before the table linking back to the syntax chapter and
> describing the newly added rules and syntax choice in the table.
>
> The nuances of floating point math suggest to me that specifying order by for
> those is in some kind of gray area and so I've marked it optional...any
> suggestions for wording (or an xref) to explain those nuances or should it just
> be shown non-optional like the others?  Or not shown at all?
>
> The novelty of my examples is up for bikeshedding.  I didn't want anything too
> long so a subquery didn't make sense, and I was trying to avoid duplication as
> well as multiple lines - hence creating a CTE that can be copied onto all of
> the example queries to produce the noted result.
>
> I added a DISTINCT example to array_agg because it is the first aggregate on
> the page and so hopefully will be seen during a cursory reading.  Plus,
> array_agg is the go-to function for doing this kind of experimentation.

I like this idea, though the examples seemed too detailed so I skipped
them.  Here is the trimmed-down patch I would like to apply.