Re: Subquery to select max(date) value

On Tue, 12 Feb 2019, Ken Tanzer wrote:

> If that's getting you what you want, then great and more power to you. It
> looks like you'll only get people who have a next_contact in your target
> window there. You might also consider something like this...
>
> select
> p.person_id,
> p.lname,
> p.fname,
> p.direct_phone,
> o.org_name,
> a.next_contact
> from
> people as p
> LEFT JOIN organizations o USING (person_id)
> LEFT JOIN (
> SELECT
> DISTINCT ON (person_id)
> person_id,
> next_contact
> FROM activities a
> -- WHERE ???
> ORDER BY person_id,next_contact DESC
> ) a USING (person_id)
> ;

I modified this to restrict the time and ignore nulls by replacing the
question marks:

WHERE a.next_contact <= 'today' and a.next_contact > '2018-12-31' and
a.next_contact is not null

For a reason I've not yet found, the last condition is not observed; i.e.,
those rows with null next_contact dates appear in the results. Position in
the sequence makes no difference. What might cause this?

Regards,

Rich