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From: David Griffiths <dgriffiths@boats.com>
To: pgsql-sql@postgresql.org
Subject: Re: SELECT... FOR UPDATE
Date: Fri, 15 Feb 2002 17:49:49 -0800
Message-ID: <a4kdul$2eln$1@jupiter.hub.org> (raw)
References: <20020215155107.1e405665.postgres@vsservices.com>

SELECT .... FOR UPDATE;

locks all records returned from the SELECT. Anyone who tries to update any
one of those records will block until you commit, rollback (or the
connection is dropped and a rollback issued).

It will ensure that no-one can modifiy the record(s).

David
"GB Clark" <postgres@vsservices.com> wrote in message
news:20020215155107.1e405665.postgres@vsservices.com...
> Hi,
>
> Can anyone give me a couple of examples or a explanation of select for
update is supposed to work?
>
> I've looked in the manual and the locking stuff is confusing (or it could
just be me not understanding..))
>  and neither of my SQL books go into any type of detail on locking.
>
> What I want to do is select a record, do something and then update that
record to reflect the outcome
> of the processing with 0% chance of another process doing the same thing.
Is this possiable?
>
> my idea:
>
> BEGIN
> SELECT * FROM table1 WHERE record_id = '290202' FOR UPDATE
> -- Do processing here
> UPDATE table1 SET flag1 = '11' WHERE record_id = '290202'
> COMMIT
>
> Just looking for more information....
>
> Thanks,
>
> GB
>
> --
> GB Clark II             | Roaming FreeBSD Admin
> gclarkii@VSServices.COM | General Geek
>            CTHULU for President - Why choose the lesser of two evils?
>
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