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help / color / mirror / Atom feedFrom: David G. Johnston <[email protected]>
To: Rich Shepard <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: Extract only maximum date from column
Date: Thu, 4 Dec 2025 13:03:35 -0700
Message-ID: <CAKFQuwZEWkgQeWSB7nqzBjHS8kP7kvouT6jhKvfe_G2e3cJvOQ@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
On Thursday, December 4, 2025, Rich Shepard <[email protected]>
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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To: [email protected]
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Subject: Re: Extract only maximum date from column
In-Reply-To: <CAKFQuwZEWkgQeWSB7nqzBjHS8kP7kvouT6jhKvfe_G2e3cJvOQ@mail.gmail.com>
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