[postgis-users] avoid duplicates with lateral auto join
Olivier Leprêtre
o.lepretre at gmail.com
Sun May 28 08:21:04 PDT 2017
Very smart Darafei, thanks !
I was not aware of the ctid column
De : postgis-users [mailto:postgis-users-bounces at lists.osgeo.org] De la part de Darafei "Kom?pa" Praliaskouski
Envoyé : dimanche 28 mai 2017 16:30
À : PostGIS Users Discussion
Objet : Re: [postgis-users] avoid duplicates with lateral auto join
Add something like
where o.ctid < t1.ctid
to the inner query.
Also, the query doesn't need to be lateral join,
select
a.name,
b.name
from t1 a, t1 b
where ST_Intersects(a.geom, b.geom)
and a.ctid < b.ctid;
should work the same.
вс, 28 мая 2017 г. в 15:18, Olivier Leprêtre <o.lepretre at gmail.com>:
Hi,
Doing a lateral auto join return cross results like A,B and B,A. Is there a simple trick to avoid that ?
To explain : in such query
select o.name,nam1 from
t1 o,
lateral (select o.name,t1.nam nam1 from t1
where st_overlaps(o.geom,t1.geom)) lat
order by o.name
I get results like
polygon1 polygon2
polygon2 polygon1
because polygon1 overlap polygon2 and conversely.
how could I get only one of those pairs ?
Thanks,
Olivier
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