Re: Most recent row

On Fri, May 5, 2017 at 1:25 AM, Gary Stainburn <
gary(dot)stainburn(at)ringways(dot)co(dot)uk> wrote:

> This question has been asked a few times, and Google returns a few
> different
> answers, but I am interested people's opinions and suggestions for the
> *best*
> wat to retrieve the most recent row from a table.
>
> My case is:
>
> create table people (
> p_id serial primary key,
> ......
> );
>
> create table assessments (
> p_id int4 not null references people(p_id),
> as_timestamp timestamp not null,
> ......
> );
>
> select p.*, (most recent) a.*
> from people p, assessments a
> ..
> ;
>

​I would start with something using DISTINCT ON and avoid redundant data.
If performance starts to suck I would then probably add a field to people
where you can record the most recent assessment id and which you would
change via a trigger on assessments.

(not tested)​

​SELECT DISTINCT ON (p) p, a
FROM people p
LEFT JOIN ​assessments a USING (p_id)
ORDER BY p, a.as_timestamp DESC;

David J.