[postgis-users] getting different geometries with geomunion()

[Hentschel, Markus]

Hi everyone,

can't find a solution in the archive, but maybe somebody asked this before:

With GeomUnion postgis returns one single geometry. In my case the returned geometry is a multipolygon containing multiple geometries which don't adjoin. Is it possible to get one polygon for each area? Unfortunately there is no attribute to group by. The only attribute is the geometry, but I can't use the aggregated the_geom in the GROUP BY clause.

For example, if you have a polygon database of all states of the US and your statement is this:

SELECT geomunion(the_geom)
FROM states
WHERE name like 'I%'

the result would be *one* multipolygon containing Illinois and Indiana, but also Idaho. How can you get seperated polygons containing only the respectively adjacent geometries?  

thanks and greetings

Markus



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