Message-ID: <44459EAF.2030601@calorieking.com>
Date: Wed, 19 Apr 2006 10:21:35 +0800
From: Christopher Kings-Lynne <chris.kings-lynne@calorieking.com>
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To: PFC <lists@peufeu.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, mario.splivalo@mobart.hr,
	pgsql-performance@postgresql.org
Subject: Re: SELECT FOR UPDATE performance is bad
References: <1145365720.18469.35.camel@localhost.localdomain>
	<13037.1145370658@sss.pgh.pa.us>
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	<13609.1145374386@sss.pgh.pa.us> <op.s77qveghcigqcu@apollo13>
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> Suppose you have a table codes :
> (
>     game_id    INT,
>     code        TEXT,
>     used        BOOL NOT NULL DEFAULT 'f',
>     prize        ...
>     ...
>     PRIMARY KEY (game_id, code)
> )
> 
>     Just UPDATE codes SET used='t' WHERE used='f' AND game_id=... AND 
> code=...
> 
>     Then check the rowcount : if one row was updated, the code was not 
> used yet. If no row was updated, the code either did not exist, or was 
> already used.

You can use a stored procedure with exceptions no?

Try this:

http://www.postgresql.org/docs/8.1/interactive/plpgsql-control-structures.html#PLPGSQL-UPSERT-EXAMPLE

Chris