[postgis-users] Need help concatentating 60, 000 polygon geometries

[Paul Ramsey]

Counter-intuitively, do this (collecting all your smaller geometries 
into one big one to test other features for containment) is probably 
going to make your system SLOWER for any given containment query.

As a collection of small objects, the index system can partition out the 
few small objects that need to be tested for any given candidate 
feature. As a single large object, the same large object will have to be 
de-serialized, and every edge of that object tested against the candidate.

Paul

Kevin Neufeld wrote:
> Scott Schulthess wrote:
>>
>> Hello everyone,
>>
>>  
>>
>> I have a table with 60,000 rows.
>>
>>  
>>
>> Each row has a geometry field that is a polygon.
>>
>>  
>>
>> I want to concatenate all of these geometry objects into one big 
>> multipolygon, or at the very least, a polygon, so I can query easily 
>> on one geometry object to see if a point lies within that multipolygon.
>>
>>  ...
>>
> Use collect(geometry set).
> 
> CREATE TABLE my_multi_polygon AS
>  SELECT collect(geom) AS geom
>  FROM my_poly_table;
> 
> -------------
> Kevin Neufeld
> Software Developer
> Refractions Research Inc.
> 300-1207 Douglas St.
> Victoria, B.C., V8W 2E7
> 
> Phone: (250) 383-3022
> Email: kneufeld at refractions.net
> 
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-- 

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