[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)
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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