From: Wolfgang Keller <feliphil@gmx.net>
To: pgsql-sql@postgresql.org
Subject: Re: Correct implementation of 1:n relationship with n>0?
Date: Tue, 30 Apr 2013 20:19:22 +0200
Message-ID: <20130430201922.be3c8b2294ccbf48fbff362f@gmx.net> (raw)
In-Reply-To: <20130430163905.77d43412c0176c3d9ebd8d90@gmx.net>
References: <20130430163905.77d43412c0176c3d9ebd8d90@gmx.net>
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> It hit me today that a 1:n relationship can't be implemented just by a
> single foreign key constraint if n>0. I must have been sleeping very
> deeply not to notice this.
>
> E.g. if there is a table "list" and another table "list_item" and the
> relationship can be described as "every list has at least one
> list_item" (and every list_item can only be part of one list, but
> this is trivial).
<duck>
BTW: If every list_item could be part of any number (>0) of lists, you
get a n:m relationship with a join table and then the issue that each
list_item has to belong to at least one list arises as well.
Maybe there should also be a standard solution documented somewhere for
this case, too.
</duck>
Sincerely,
Wolfgang
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To: pgsql-sql@postgresql.org
Cc: feliphil@gmx.net
Subject: Re: Correct implementation of 1:n relationship with n>0?
In-Reply-To: <20130430201922.be3c8b2294ccbf48fbff362f@gmx.net>
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