[postgis-users] using && operator

[Jan Saalbach]

Thank you Aman for your detailed answer. I understand why it did not  
work in the first place now. And yes, I need to learn SQL properly.

Regards,
Jan


Zitat von Aman Verma <aman.verma at mcgill.ca>:

> Hi,
>
> It looks like you're having a little bit of trouble with the SQL.  
> That is understandable though, your problem is a little tricky,  
> because it requires you to nest a query.
>
> You should first note that it is not possible to have two FROM  
> statements in a single query. Start by breaking down the problem  
> into individual parts:
>
> 1) You need to collect both geometry columns each into a single  
> collection. You can do this with two separate queries:
>
>
> select st_collect(pkt) as first_set from pktbsp1;
> select st_collect(pkt) as second_set from pktbsp2;
>
> 2) Now, you need to find a way to have the result of both these  
> tables in a single place. This is done by nesting the two above  
> queries into another query.
>
> select x.first_set, y.second_set from
> (select st_collect(pkt) as first_set from pktbsp1) x, -- I could  
> have used JOIN instead of a comma.
> (select st_collect(pkt) as second_set from pktbsp2) y;
>
> If you're having trouble figuring out how the query nesting works, I  
> suggest brushing up your SQL at sqlzoo.net.
>
> 3) Now, you can compare these two geometries. So the full query is:
>
> select x.first_set && y.second_set from -- Note that st_intersects  
> (x.first_set,y.second_set) would be fine too
> (select st_collect(pkt) as first_set from pktbsp1) x,
> (select st_collect(pkt) as second_set from pktbsp2) y;
>
> That will return a single row with a single column: t or f.
>
> Hope that helps,
>
> aman
>
>
> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net  
> [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of  
> Jan Saalbach
> Sent: August 20, 2010 10:02 AM
> To: PostGis Users List
> Subject: [postgis-users] using && operator
>
> Hi List,
> how do I check if two 3d-point sets overlap? I see the && operator
> should be able to compare the bounding boxes, but how do I do it? I
> can not get the && or ST_Intersects function to work. Here is what I
> am trying to do:
>
> SELECT ST_Collect(pkt) FROM pktbsp && ST_Collect(pkt) FROM pktbsp2;
>
> pkt are GeometryColumns filled with 3dpoints. pktbsp and pktbsp2 are
> the respective tables.
>
> How can I check this?
>
> Reagrds,
> Jan
>
>
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