[postgis-users] selecting geometries, using 2 polygons

[strk]

On Tue, Apr 28, 2009 at 03:16:04PM +0200, Malm Paul wrote:
> Hi,
> I have 2 polygons (rectangeles) p1 and p2, they intersect each other.
> I would like to select all geometries within p1 excluding all geometries within p2.
> 
> How can I do this with postGIS and SQL ?

I suggest you first get p3 as difference(p1, p2),
then use ST_intersect on p3 and your geom column.

You should be careful in the way you construct the query 
so that difference() is computed only once, and make sure
the gist index is used by ST_intersect.

--strk;

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