[postgis-users] Merge all polygons from a dataset

Obe, Regina robe.dnd at cityofboston.gov
Fri Aug 1 04:15:33 PDT 2008

How were you using ST_Union and what exactly do you mean by no result.
no result as it looks blank?  If you are using something like PgAdmin
III - it will look blank because it exceeds the buffer supported by
PgAdmin III.
SELECT the_geom is null 
FROM (somequery or table) as foo
will tell you if its actually returning no geometry
Hope that helps,


From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
Sent: Friday, August 01, 2008 6:12 AM
To: postgis-users at postgis.refractions.net
Subject: [postgis-users] Merge all polygons from a dataset

Hello everybody,

I've converted a shapefile of Europe to PostGIS. I would like to merge
all the countries together so that I only have one polygon left, the
whole contour of Europe. I have tried ST_Union that gives me no result.
I've tried several other functions to no avail. Does anybody know how I
should proceed?

Many thanks,


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