Re: Extract only maximum date from column

On 12/4/25 1:39 PM, Rich Shepard 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

Would the below work?:

WITH lc AS (SELECT person_nbr, max(next_contact) AS last_contact from 
contacts where next_contact > '2025-11-01' group by c.person_nbr)
select p.person_nbr, p.company_nbr, lc.last_contact from people AS p 
join lc on p.person.nbr = lc.person_nbr;

> 
> Regards,
> 
> Rich
> 
> 

-- 
Adrian Klaver
adrian.klaver@aklaver.com