[postgis-devel] Non-Join Join

[Obe, Regina]

The below is usually (shall I say wicked fast) compared to the other
approach

-----Original Message-----
From: postgis-devel-bounces at postgis.refractions.net
[mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf Of
Martin Davis
Sent: Friday, July 18, 2008 5:23 PM
To: PostGIS Development Discussion
Subject: Re: [postgis-devel] Non-Join Join

Good suggestion - that's another way. 

I wonder which is faster (or if there's any difference)?

BTW, wouldn't this be better posted to postgis-users?

Obe, Regina wrote:
> How about
>
> SELECT A.gid, A.geom, A.letter
> FROM (SELECT * FROM lettertable WHERE letter = 'A') A 
> LEFT JOIN (SELECT * FROM lettertable WHERE letter = 'B') B 
> 	ON ST_DWithin(A.the_geom, B.the_geom, 1000)
> WHERE B.gid IS NULL;
>
> -----Original Message-----
> From: postgis-devel-bounces at postgis.refractions.net
> [mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf Of
Paul
> Ramsey
> Sent: Friday, July 18, 2008 5:06 PM
> To: PostGIS Development Discussion
> Subject: [postgis-devel] Non-Join Join
>
> Brain freeze:
>
> Give a table
>
> gid integer
> geom geometry
> letter varchar
>
> where letter is a single letter,
>
> how to efficiently find all the instances of the letter 'A' that are
> more than 1000m from any letter 'B'.
>
> P.
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-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022

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