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From: Andreas Kretschmer <andreas@a-kretschmer.de>
To: pgsql-sql@lists.postgresql.org
Subject: Re: Windowing ?
Date: Mon, 11 Dec 2017 18:15:56 +0100
Message-ID: <f02993c7-c740-e99b-e0e2-010a36ded92d@a-kretschmer.de> (raw)
In-Reply-To: <5a2ebbc9.8a1f1c0a.ea0ea.7b4a@mx.google.com>
References: <5a2ebbc9.8a1f1c0a.ea0ea.7b4a@mx.google.com>



Am 11.12.2017 um 18:09 schrieb Olivier Leprêtre:
>
> Hi,
>
> I have a table describing sort of ordered road segments and their 
> associated weight. I would like to calculate weight deltas between two 
> consecutive segments. Problem is to substract previous from current 
> row and reuses result as input for the next row.
>

You can use the lag() - function.

select ..., lag(weight) over (partition by road order by segment) ...



Regards, Andreas

-- 
2ndQuadrant - The PostgreSQL Support Company.
www.2ndQuadrant.com

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