Subject: Re: plpgsql arrays
From: Simon Riggs <simon@2ndQuadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Matthew Wakeling <matthew@flymine.org>, pgsql-performance@postgresql.org
In-Reply-To: <28595.1238767442@sss.pgh.pa.us>
References: <alpine.DEB.2.00.0904031420470.21772@aragorn.flymine.org>
	<603c8f070904030647u1c92e13ew53612ac0011ed7c1@mail.gmail.com>
	<alpine.DEB.2.00.0904031455210.21772@aragorn.flymine.org>
	<28595.1238767442@sss.pgh.pa.us>
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Date: Fri, 03 Apr 2009 18:30:39 +0100
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On Fri, 2009-04-03 at 10:04 -0400, Tom Lane wrote:
> Matthew Wakeling <matthew@flymine.org> writes:
> > On Fri, 3 Apr 2009, Robert Haas wrote:
> >> Why not just use SQL to do the join?
> 
> > Because the merge condition is:
> 
> > WHERE l1.start <= l2.end AND l2.start <= l1.end
> 
> > and merge joins in postgres only currently cope with the case where the 
> > merge condition is an equals relationship.

(snip)

> I don't actually believe that a standard merge join algorithm will work
> with an intransitive join condition ...

I think it's a common enough problem that having a non-standard join
algorithm written for that case would be interesting indeed.

-- 
 Simon Riggs           www.2ndQuadrant.com
 PostgreSQL Training, Services and Support