[postgis-users] Centroid out a list of points

[strk]

On Fri, Jun 12, 2009 at 10:34:21AM +0100, Pedro Doria Meunier wrote:
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> Thank you Nicklas for your advice! That actually accomplishes it with
> a notable exception:
> 
> Altough the table has a gist index on the geom column the query is
> always executed in Seq Scan mode...
> 
> I ask the gurus which fx is causing this, st_centroid or st_collect ?

It's the WHERE clause driving access strategy.
If you're giving no conditions of course sequential scan is faster.
Only reason to use the gist geometry index is if you use the &&
operator in the WHERE clause, and the analizer finds it to be
enough selective to prefere index vs. sequential scan.

--strk;

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