Sv: Re: Is ORDER BY in sub-query preserved when outer query is only projection?

På søndag 14. januar 2018 kl. 13:30:29, skrev Francisco Olarte <
folarte(at)peoplecall(dot)com <mailto:folarte(at)peoplecall(dot)com>>:
Andreas:

On Sun, Jan 14, 2018 at 1:03 PM, Andreas Joseph Krogh
<andreas(at)visena(dot)com> wrote:
> SELECT q.* FROM (
>   SELECT comp.id, comp.name
>   FROM company comp JOIN req r ON r.company_id = comp.id
>   ORDER BY LOWER(comp.name) ASC
> ) AS q
> ORDER BY r.status ASC
>
> What I'm trying to do here is to order by some status (which may be only 1
of 3 values, for instance OPEN, IN_PROGRESS, CLOSED), then order by
company-name so I get results for each status sorted by company-name.
>
> Is this kind of sort stable, can I assume the pre-sorted result's order is
preserved so I achieve what I want?

I doubt it is mandated to be stable. But IIRC you can sort by a
non-returned field, so you should be able to do it in just one query (
http://sqlfiddle.com/#!17/aaa62/3 )

I would try

 SELECT comp.id, comp.name
 FROM company comp JOIN req r ON r.company_id = comp.id
 ORDER BY  r.status ASC, LOWER(comp.name) ASC

Francisco Olarte.
 
Thanks, but my real query is more complex and I need to sort on a custom
coposite type so I think I need an outer query for that, see my post
here: http://www.postgresql-archive.org/ORDER-BY-custom-type-td6000437.html
 
Do you see any solution sorting on a composite type without using an outer
query?
 
-- Andreas Joseph Krogh
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