From: | Bruno Wolff III <bruno(at)wolff(dot)to> |
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To: | Joachim Trinkwitz <jtr(at)uni-bonn(dot)de> |
Cc: | pgsql-sql(at)postgresql(dot)org |
Subject: | Re: INSERT only under certain conditions (SELECT) |
Date: | 2002-07-09 12:18:36 |
Message-ID: | 20020709121836.GA30146@wolff.to |
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Thread: | |
Lists: | pgsql-sql |
On Mon, Jul 08, 2002 at 17:49:56 +0200,
Joachim Trinkwitz <jtr(at)uni-bonn(dot)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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