[postgis-users] Centroid out a list of points

[Pedro Doria Meunier]

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Strk, you're so on the money! :)
Thank you very much! The query now runs in ~40ms :P

I also wish to thank everyone gracious enough to have shared their
thoughts.

BR,

Pedro Doria Meunier
GSM: +351 96 17 20 188
Skype: pdoriam
 



strk wrote:
> On Fri, Jun 12, 2009 at 10:54:11AM +0100, Pedro Doria Meunier
> wrote:
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>>
>> Thank you Strk.
>>
>> The actual query is as thus:
>>
>> select astext(st_centroid(st_collect(coordinates))) from units
>> where customer_id=someid
>>
>> So there's a 'where' clause in it :]
>
> The 'where' clause specifies a condition on the 'customer_id'
> field. The only index the planner might use would be on on that
> column. Have an index there (looks like the analizer already thinks
> it'd be worth using, estimating only 9 rows selectivity for that
> clause, where 4 are returned in reality)
>
> --strk;
>
>> EXPLAIN ANALYZE tells me:
>>
>> "Aggregate  (cost=49790.11..49790.13 rows=1 width=25) (actual
>> time=524.380..524.381 rows=1 loops=1)" "  ->  Seq Scan on units
>> (cost=0.00..49790.09 rows=9 width=25) (actual
>> time=445.782..524.231 rows=4 loops=1)" "        Filter:
>> (customer_id = 20)" "Total runtime: 524.451 ms"
>>
>> The runtime is a bit stiff, don't you agree? ;-)
>
> Probably. How many rows does the table have ?
>
> --strk;
>
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