[postgis-devel] Non-Join Join

Obe, Regina robe.dnd at cityofboston.gov
Fri Jul 18 14:13:02 PDT 2008

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)

-----Original Message-----
From: postgis-devel-bounces at postgis.refractions.net
[mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf Of Paul
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'.

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