Re: Extract only maximum date from column

On Thursday, December 4, 2025, Rich Shepard <rshepard(at)appl-ecosys(dot)com>
wrote:

> On Thu, 4 Dec 2025, David G. Johnston wrote:
>
> I would go with a lateral join subquery of the contracts table. Using an
>> aggregates to perform ranking is an anti-pattern. You want the contract
>> ranked first when ordered by contract_date. Either use a window function
>> to explicitly rank the contracts or use a limit/fetch clause to simply
>> return the first ordered one.
>>
>
> David,
>
> I'm closer, but still missing the proper syntax:
>
> select p.person_nbr, p.company_nbr, c.next_contact
> from people as p, contacts as c
> join lateral (select max(c.next_contact) as last_contact
> where p.person_nbr = c.person_nbr and
> last_contact >= '2025-11-01'
> )
> c on true;
>
> resulting in:
> psql:companies-contacted-2025.sql:9: ERROR: aggregate functions are not
> allowed in FROM clause of their own query level
> LINE 3: join lateral (select max(c.next_contact) as last_contact
>

As mentioned, the aggregate max should be avoided - you aren’t doing
statistics, you are ranking.

Select person.*, lastcontact.* from person join lateral (select contact.*
from contact where contact.person_id=person.person_id order by
last_contact_date desc limit 1) as lastcontact on true;

David J.