Date: Wed, 24 Nov 2010 21:53:16 +0100
From: Louis-David Mitterrand <vindex+lists-pgsql-sql@apartia.org>
To: pgsql-sql@postgresql.org
Subject: Re: "compressing" consecutive values into one
Message-ID: <20101124205316.GA16666@apartia.fr>
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References: <20101123151918.GA22094@apartia.fr>
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On Tue, Nov 23, 2010 at 04:19:18PM +0100, Louis-David Mitterrand wrote:
> Hi,
> 
> On time series price data I'm trying to remove consecutive identical
> prices and keep only the latest. I tried:
> 
> 	delete from price where id_price in (select t.id_price2 from (select
> 			first_value(p.id_price) over w as id_price1,
> 			nth_value(p.id_price, 2) over w as id_price2,
> 			first_value(p.price) over w as price1,
> 			nth_value(p.price,2) over w as price2
> 			from price p
> 			window w as (partition by p.id_rate,p.id_cabin_category,p.id_cruise
> 			order by p.id_price desc rows between unbounded preceding and
> 			unbounded following)) as t where price1 = price2);
> 
> and it mostly works but I have to do several runs to completely
> eliminate identical consecutive prices.

Actually I found the answer to my own question. It's the WINDOW lag/lead
functions that I needed and this time one pass is enough:

	delete from price where id_price in (   
	select t.id_price1 from (select
			lead(p.id_price) over w as id_price1,
			lead(p.price) over w as price1,
			p.id_price, p.price 
			from price p
			window w as (partition by p.id_rate,p.id_cabin_category,p.id_cruise
			order by p.id_price rows between unbounded preceding and
			unbounded following)) 
		as t where t.price = t.price1);