[postgis-users] bringing together two polygon datasets

[Sandro Santilli]

On Tue, May 29, 2012 at 09:48:11AM +0200, Falko Engel wrote:
> Dear list,
> 
> I know this is a very basic question, but I can't find any example
> online for this:
> 
> I would like to combine two and possibly more (non intersecting)
> polygon datasets into one. This opperation in called "patch" in the
> ESRI-world. Could someone give me an example?

One item for each item in each dataset ?

CREATE TABLE combined AS SELECT
 1 as dataset_id, gid, the_geom FROM dataset1
 UNION ALL
 2 as dataset_id, gid, the_geom FROM dataset2;

Combine items with the same "id" from each dataset ?

CREATE TABLE combined AS SELECT
 a.id, st_union(a.the_geom, b.the_geom)
 FROM dataset1 a, dataset2 b
 WHERE a.id = b.id;

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