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Message-ID: <4AB8DA96.2090502@gmail.com>
Date: Tue, 22 Sep 2009 08:09:26 -0600
From: Rob Sargent <robjsargent@gmail.com>
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To: "A. Kretschmer" <andreas.kretschmer@schollglas.com>
CC: pgsql-sql@postgresql.org
Subject: Re: selecting latest record
References: <20090922094457.GA24885@apartia.fr>
	<20090922100846.GD5415@a-kretschmer.de>
In-Reply-To: <20090922100846.GD5415@a-kretschmer.de>
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Let's say there's an index on the date column: Does the where clause 
approach necessarily out perform the distinct on version? Hoping the OP 
has enough data to make analyse useful.

A. Kretschmer wrote:
> In response to Louis-David Mitterrand :
>   
>> Hi,
>>
>> I have a simple table 
>>
>> price(id_product, price, date) 
>>
>> which records price changes for each id_product. Each time a price
>> changes a new tuple is created.
>>
>> What is the best way to select only the latest price of each id_product?
>>     
>
> There are several ways to do that, for instance with DISTINCT ON (only
> postgresql):
>
> test=*# select * from price ;
>  id_product | price |   datum
> ------------+-------+------------
>           1 |    10 | 2009-09-01
>           1 |    12 | 2009-09-10
>           2 |    11 | 2009-09-10
>           2 |     8 | 2009-09-13
> (4 rows)
>
> test=*# select distinct on (id_product) id_product, price from price order by id_product, datum desc;
>  id_product | price
> ------------+-------
>           1 |    12
>           2 |     8
> (2 rows)
>
> Andreas
>