Re: Extract only maximum date from column
| От | David G. Johnston |
|---|---|
| Тема | Re: Extract only maximum date from column |
| Дата | |
| Msg-id | CAKFQuwZEWkgQeWSB7nqzBjHS8kP7kvouT6jhKvfe_G2e3cJvOQ@mail.gmail.com обсуждение исходный текст |
| Ответ на | Extract only maximum date from column (Rich Shepard <rshepard@appl-ecosys.com>) |
| Ответы |
Re: Extract only maximum date from column
Re: Extract only maximum date from column |
| Список | pgsql-general |
On Thursday, December 4, 2025, Rich Shepard <rshepard@appl-ecosys.com> wrote:
I want the script to extract only the maximum `next_contact' date and
haven't learned how to do this from my reading of web sites.
The script:
select p.person_nbr, p.company_nbr, c.next_contact
from people as p, contacts as c
where c.next_contact >= '2025-11-01'
group by p.person_nbr, p.company_nbr, c.next_contact
order by p.person_nbr, p.company_nbr, max(c.next_contact);
returns all contacts rather than only the latest one.
Is using a sub-select the proper way?
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.
You also seem to have completely missed joining people to contracts - suggest using explicit “join” clauses to make that error less likely.
David J.
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