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From: Rich Shepard <[email protected]>
To: [email protected] <[email protected]>
Subject: Re: Extract only maximum date from column
Date: Thu, 4 Dec 2025 13:39:56 -0800 (PST)
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAKFQuwZEWkgQeWSB7nqzBjHS8kP7kvouT6jhKvfe_G2e3cJvOQ@mail.gmail.com>
References: <[email protected]>
	<CAKFQuwZEWkgQeWSB7nqzBjHS8kP7kvouT6jhKvfe_G2e3cJvOQ@mail.gmail.com>

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

Regards,

Rich

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