[Qgis-developer] have aggregate/window expressions ever been discussed?

Régis Haubourg regis.haubourg at eau-adour-garonne.fr
Tue May 27 06:55:21 PDT 2014

giohappy wrote
> I agree with all of you about not reinventing the wheel and, yes, let's
> not
> fragment QGIS' capabilities on data querying/filtering/etc.

I agree totally.SQLITE could be a very powerfull basement to build user
oriented functions. But we need to be sure that it won't add *under the
hood* tricks. 

My first need here would be to be able to intersect two layers (Polygon X
Polygon ) and compute overlap ratios and unique relations of objects. 
I made a PGSQL procedure for that, and wish I could offer the same in QGIS
client, whatever datasource the user inputs. 
My latest tests converged to using processing python script, reading layers
in OGR and using Spatial SQL capacities for intersect and aggregate steps.
The hard part is how to get datasource definition from QGIS and make OGR
read it. The aggregate capacities of SQLite are easy to handle.  If we could
directly use qgis layers as OGR virtual layers, that would be sooo simple. 


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