[postgis-users] Re: Aggregate?

[Stephen Crawford]

That's exactly what I needed.  Thanks a lot.  -Steve

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Paul
Ramsey
Sent: Thursday, March 01, 2007 4:41 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Re: Aggregate?

Stephen Crawford wrote:

> I don't quite understand this part:
> "Use collect(geometryn(the_geom, 1)) id your data is specified as 
> singular multigeometries."

If you've loaded your data from shape files, then your POLYGON features will
all be MULTIPOLYGON by default, even if they all have only one part. So when
you Collect() them, you'll get a GEOMETRYCOLLECTION instead of a
MULTIPOLYGON.

GeometryN(the_geom,1) turns one-part MULTIPOLYGONS into simple POLYGONS, so
that when you Collect() the result is a MULTIPOLYGON.

> Also, if I want to keep a few of the record for based on another 
> another value, should this work?:
> 
> SELECT name, party, collect(the_geom)) AS the_geom,
>     FROM constituencies
>    GROUP BY constituencies.name, constituencies.party;

This will return one collection for each distinct combination of name and
party.

Paul

-- 

   Paul Ramsey
   Refractions Research
   http://www.refractions.net
   pramsey at refractions.net
   Phone: 250-383-3022
   Cell: 250-885-0632
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