[postgis-users] I'm missing something

[Bob Pawley]

I tried this -

Insert into graphics.process_dgm(the_geom)
 Select   ST_Union(the_geom)
 from tank_lin;

and got the error "Unknown geometry type: 0"

Bob
----- Original Message ----- 
From: "Paul Ramsey" <pramsey at cleverelephant.ca>
To: "PostGIS Users Discussion" <postgis-users at postgis.refractions.net>
Sent: Tuesday, May 20, 2008 9:51 AM
Subject: Re: [postgis-users] I'm missing something


> You don't want the GROUP BY. It is grouping the union op on distinct
> geometry... ie, one per row. Remove it and you'll get what you want,
> one output row.
>
> P
>
> On Tue, May 20, 2008 at 8:49 AM, Bob Pawley <rjpawley at shaw.ca> wrote:
>> Hi
>>
>> I am attemptijng to use the ST_Union function to collapse three rows from 
>> a
>> table called tank_lin into one row in table called process_dgm.
>>
>> Here's what I used -
>> Insert into graphics.process_dgm(the_geom)
>> Select   ST_Union(the_geom)
>> from tank_lin
>> Group by tank_lin.the_geom;
>>
>> The result is three rows inserted into process_dgm, each row appearing to 
>> be
>> simple copies of each of the original rows.
>> I also attempted group by another column but received error 'unknown
>> geometry'.
>>
>> I also tried STR_LineMerge with similar results.
>>
>> What am I not considering?
>>
>> Bob
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