[Qgis-user] spatialite (and postgis) queries

[Ricardo Filipe Soares Garcia da]

Hi all

Thanks for your positive (and fast!) replies.
I'll be giving the RT Sql layer plugin a try and I'll also investigate
whether this functionality is available (using python scripting) with
spatialite layers.

Jurgen:

thanks for the SQL EXISTS tip. I have to brush up on my SQL ;)
Still I didn't know that it is possible to use other table names in
QGIS's Query Builder.



On Thu, Sep 30, 2010 at 1:27 PM, Jürgen E. <jef at norbit.de> wrote:
> Hi Carson,
>
> On Thu, 30. Sep 2010 at 13:18:46 +0100, Carson Farmer wrote:
>> http://www.carsonfarmer.com/?p=713
>> and the RT Sql Layer plugin
>> > 1 - Is it possible to build a query where two (or more) layers are
>> > involved? Something like:
>> >
>> > SELECT a.*
>> > FROM a, b
>> > WHERE Contains(b, a)
>
> and that simple case can be expressed as exists expression in the query builder
> (for postgres and spatialite).  Create a layer from a and use following query
> string:
>
>        exists (select * from b where contains(b.geom,a.geom))
>
> Creating views is another option (but you still need a unique 32bit integer
> primary key for the feature ids, which might be hard to generate in some
> cases).
>
>
> Jürgen
>
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Ricardo Garcia Silva