[postgis-users] I'm missing something

[Paul Ramsey]

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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