Date: Wed, 2 Oct 2013 22:10:56 -0700 (PDT)
From: gmb <gmbouwer@gmail.com>
To: pgsql-sql@postgresql.org
Message-ID: <1380777056063-5773196.post@n5.nabble.com>
In-Reply-To: <1380762368253-5773171.post@n5.nabble.com>
References: <1380751468173-5773160.post@n5.nabble.com>
 <1380762368253-5773171.post@n5.nabble.com>
Subject: Re: Help needed with Window function
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David Johnston wrote
> Basic idea: use ORDER BY in the window to auto-define a range-preceding
> frame.  Create an array of all dates (tags in the example) that match with
> positive amounts.  Negative amounts get their matching tag added to the
> array as NULL.  The provided function looks into the generated array and
> returns the last (closest to the current row in the frame) non-null
> date/tag in the array which ends up being the date/tag matching the last
> positive amount in the frame.
> 
> David J.

Hi David,

Thanks for your reply.
This is an approach I also considered, but hoped for a solution without the
expense (albeit small) of having to create a function. 
Just wanted to confirm that I'm not missing a simpler solution (my knowledge
in terms of window functions is rather limited).
Until something better comes along, I'll implement the solution as suggested
here.

Regards

GMB


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