From: Bruno Wolff III <bruno@wolff.to>
To: Joachim Trinkwitz <jtr@uni-bonn.de>
Cc: pgsql-sql@postgresql.org
Subject: Re: INSERT only under certain conditions (SELECT)
Date: Tue, 9 Jul 2002 07:18:36 -0500
Message-ID: <20020709121836.GA30146@wolff.to> (raw)
In-Reply-To: <87y9cm1aor.fsf@waffel.germanistik.uni-bonn.de>
References: <874rfb6mqe.fsf@wabe.germanistik.uni-bonn.de>
<20020708124013.GA30022@wolff.to>
<87y9cm1aor.fsf@waffel.germanistik.uni-bonn.de>
On Mon, Jul 08, 2002 at 17:49:56 +0200,
Joachim Trinkwitz <jtr@uni-bonn.de> wrote:
>
> Now I want to allow a user with id 123 only to insert a row in T if he
> doesn't choose values from L with same 'art' and 'semester' values --
> in the examples user 123 has already chosen a kvvnr from semester
> 2002ws in category 'art', so he shouldn't be allowed to insert the
> values of the second row in table L.
In the database you enforce this using a unique index.
The application needs to be able to handle failures when you try to
insert a duplicate key.
If you can't afford to have a transaction fail part way through, then
anything that writes that table should do a table lock at the start
of the transaction.
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To: pgsql-sql@postgresql.org
Cc: bruno@wolff.to, jtr@uni-bonn.de
Subject: Re: INSERT only under certain conditions (SELECT)
In-Reply-To: <20020709121836.GA30146@wolff.to>
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