[postgis-users] How cutting out polygon

[Daniel Grum]

Pavel Iacovlev schrieb:
> You should translate the error message by the way if you want to get answers :)
>
> I think the problem is that your select returns multiple
> rows(geometries) but update expect 1 row. Try putting a
> ST_COLLECT/ST_UNION in your query.
>
> UPDATE fog_of_war
> SET the_geom = (    SELECT
> ST_Union(ST_Intersection(grenze_by.the_geom,ST_Expand(holzfaeller.the_geom,
> 5000)))
>                               FROM public.grenze_by grenze_by,
> public.holzfaeller holzfaeller                               WHERE
> grenze_by.the_geom && ST_Expand(holzfaeller.the_geom, 5000));
>
> 2009/9/1 Daniel Grum <daniel.grum at unibw.de>:
>   
>> Hi.
>>
>> How I can cut 4 or more differnt polygon geometries out of one big
>> geomtry[MULTIPOLYGON].
>>
>> I have one polygon (saved in the schema.tabel.column:
>>  public.fog_of_war.the_geom)
>> and from this I want to cut out  the squares, that I create with:
>>
>> SELECT ST_Intersection(grenze_by.the_geom,ST_Expand(holzfaeller.the_geom,
>> 5000))
>> FROM public.grenze_by grenze_by, public.holzfaeller holzfaeller WHERE
>> grenze_by.the_geom && ST_Expand(holzfaeller.the_geom, 5000));
>>
>> I don't want to save this cut out information in an extra table, I only want
>> to get a fog_of_war layer.
>> And You only can see what is behind this Layer(than you see the map and
>> bulidings) where the layer was cut out.
>>
>> Can I solve this problem with UPDATE like this:
>>
>> UPDATE fog_of_war
>> SET the_geom = (    SELECT
>> ST_Intersection(grenze_by.the_geom,ST_Expand(holzfaeller.the_geom, 5000))
>>                               FROM public.grenze_by grenze_by,
>> public.holzfaeller holzfaeller                               WHERE
>> grenze_by.the_geom && ST_Expand(holzfaeller.the_geom, 5000));
>>
>> I ask because I get the message: "FEHLER:  als Ausdruck verwendete
>> Unteranfrage ergab mehr als eine Zeile"
>>
>> Thanks in advance.
>>
>> --Daniel
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>>
>>     
>
>
>
>   
I have edited my SQL

The problem now is, that only the first row  will be regarded in this:

UPDATE fog_of_war
SET the_geom = ST_BuildArea(St_Collect(grenze_by.the_geom, 
ST_Expand(holzfaeller.the_geom, 3000)))
FROM public.grenze_by grenze_by, public.holzfaeller holzfaeller;

How I can regard all rows of the table in a UPDATE query --> because 
ST_Union or ST_Collect don't work in a UPDATE query

--Daniel