From: Richard Huxton <dev@archonet.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Subject: Re: Scalar in a range (but textual not numeric)
Date: Thu, 26 Feb 2004 08:03:11 +0000
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On Wednesday 25 February 2004 22:37, Tom Lane wrote:
> I wrote:
> > try writing
> > 	WHERE 'ABCDE' >= pr_min AND 'ABCDE' <= pr_max
> > 	      AND pr_min < (SELECT pr_min FROM table
> > 			    WHERE pr_min > 'ABCDE'
> > 			    ORDER BY pr_min LIMIT 1)
> > The idea here is to add an upper bound on pr_min to the index scan
> > conditions, so that the scan can stop short of the end of the index.
>
> Argh, got that backwards.  What you are missing is a *lower* bound on
> pr_min, and the index scan will therefore run from the start of the
> index up to pr_min = 'ABCDE'.  So reverse the sense of the added test:
>
> 	      AND pr_min >= (SELECT pr_min FROM table
> 			     WHERE pr_min <= 'ABCDE'
> 			     ORDER BY pr_min DESC LIMIT 1)

Aha! I was trying something like that, but couldn't get it quite right and it 
was getting too late for me to see clearly.

Thanks Tom, I'll have a play with this later today.
-- 
  Richard Huxton
  Archonet Ltd