Date: Wed, 3 Feb 2021 17:44:59 +0100
From: hubert depesz lubaczewski <depesz@depesz.com>
Sender: depesz@depesz.com
To: "David G. Johnston" <david.g.johnston@gmail.com>
Cc: Mai Peng <maily.peng@webedia-group.com>,
	Pgsql-admin <pgsql-admin@lists.postgresql.org>
Subject: Re: Design database
Message-ID: <20210203164459.GA17357@depesz.com>
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On Wed, Feb 03, 2021 at 08:35:41AM -0700, David G. Johnston wrote:
> On Wed, Feb 3, 2021 at 8:23 AM Mai Peng <[1]maily.peng@webedia-group.com> wrote:
> 
>   Hello,
> 
>   I’ve got a table name publication, and another table named publication_item.
>   Each publication_item is linked to a publication by publication_id.
>   How could I add a constraint that check each publication has one or more publication_item when a tuple is inserted ?
>   I don’t want to store items in the same table as publication because we could have 1-> n items.
> 
> [2]https://www.postgresql.org/docs/current/tutorial-fk.html

I don't think it helps. Fkey can check that publication_item contains
valid publication_id, but doesn't ensure that every publication has at
least one item.

As for the problem of OP, I think this describes working solution:
https://www.depesz.com/2017/07/03/how-to-make-sure-there-is-always-at-least-one-sub-record/

Best regards,

depesz