[postgis-devel] Non-Join Join

[Martin Davis]

I bow to the master.

Obe, Regina wrote:
> Wrong Martin.  Find all that are within 1000 with a left join using an
> indexed search and then throw out those that don't have matches.  
>
> If it has no neighbor within 1000 feet then all its neighbors must be
> more than 1000 feet away.
>
> -----Original Message-----
> From: postgis-devel-bounces at postgis.refractions.net
> [mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf Of
> Martin Davis
> Sent: Friday, July 18, 2008 5:21 PM
> To: PostGIS Development Discussion
> Subject: Re: [postgis-devel] Non-Join Join
>
> Since you're trying to find all As which are *further* than a given 
> distance from Bs, I don't think there is any "efficient" way.
>
> I think you pretty much have to do a self-join with a where condition 
> like "where distance(geomA, geomB) > 1000".  Oh, and I guess you'll need
>
> a filter condition to compare only As and Bs.
>
> Paul Ramsey wrote:
>   
>> Brain freeze:
>>
>> Give a table
>>
>> gid integer
>> geom geometry
>> letter varchar
>>
>> where letter is a single letter,
>>
>> how to efficiently find all the instances of the letter 'A' that are
>> more than 1000m from any letter 'B'.
>>
>> P.
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>>
>>   
>>     
>
>   

-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022