Subject: Re: Returning PK of first insert for second insert use.
From: Ken Corey <ken.corey@atomic-interactive.com>
To: Peter Atkins <peter.atkins@NXCD.com>
Cc: "'pgsql-sql@postgresql.org'" <pgsql-sql@postgresql.org>
In-Reply-To: <1CAD483B723BD611B0C10090274FF0685547CB@NXCDMAIL>
References: <1CAD483B723BD611B0C10090274FF0685547CB@NXCDMAIL>
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Date: 29 Jul 2002 21:04:30 +0100
Message-Id: <1027973100.2360.278.camel@kenlinux.bithub.org>
Mime-Version: 1.0

On Mon, 2002-07-29 at 20:52, Peter Atkins wrote:
> Is there a possibility of another application accessing the DB and using the
> id before my function has completed the transaction? I'm concerned with the
> possibility of cross-over of ID's if the insert hangs.
> 
> There's no way to return the id of that insert inherently, and then use it
> for the second insert? I think SQL uses something like ADD_ID, not sure.

That's the beauty of the nextval statement. The database internally
sequences requests to it so that you're kept out of harm's way.

Say process A called the function,and nextval returns 16.  The function
now continues on its way, but is not finished when process B then calls
the function (before A is done), and nextval returns 17.

So, then function called by process A returns 16, and the function
called by process B returns 17.

That means that unless the results of process B depend in some way upon
the results of process A, there's no problem.

-Ken

-- 
Ken Corey  CTO  http://www.atomic-interactive.com  07720 440 731