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

[Vincent Picavet]

Hello,

Le mardi 27 mai 2014 16:06:55, Andreas Neumann a écrit :
> Hi all,
> 
> I understand your concerns, but on the other hand - how would you treat
> all data sources equally well, if QGIS does not implement that stuff
> within QGIS for data providers that do not implement this? One could
> still write a QGIS expression to SQL compiler for those providers who
> support these functions (Matthias Kuhn proposed that).
> 
> We will need these aggregate functions in forms for information purposes
> and in the print composer for generating reports. Having to write
> Postgis-Views would work for database pros. But let's not forget that
> not all of our users are database professionals and not all of the users
> have their data in Postgis.
> 
> Personally, I don't care where these aggregate functions are implemented
> and executed, as long as they are easy to use and do not enforce the
> usage of a specific data format.

I would not be shocked if QGIS had an "official" local data format, allowing the 
user to get all features when using it, and other formats for 
interoperability.
I do not think that this would disturb users as :
* almost all software do this
* QGIS already behaves like this, with read-only data formats for examples
It would almost simplify the situation as in "use the official format or accept 
limitations".

And of course having a GeoPackage-compatible format would be a win.
This kind of change could trigger a new major version though, to make it clear 
that this is an important change.

Vincent

> 
> Andreas
> 
> Am 27.05.2014 09:21, schrieb Vincent Picavet:
> > Hello Andreas,
> > 
> > Le mardi 27 mai 2014 10:28:13, Andreas Neumann a écrit :
> >> Hi,
> >> 
> >> We would definitely need this functionality for our application modules
> >> - we need functions like "min", "max", "mean", "sum", "average" to work
> >> on 1:n relations.
> >> 
> >> Now that we have relations in QGIS, I think that aggregate functions are
> >> a logical next step. Something to seriously consider in 2.6.
> > 
> > As already stated before, I am worrying about current developments 
around
> > a lot of features looking like database features :
> > * Table joins
> > * relations
> > * "SQL-like" processing
> > * .. including aggregates
> > 
> > Implementing all these features on top of QGIS seems reinventing the
> > wheel, and database wheels are particularly hard to design and implement
> > well. I really think we should re-study the global design of such
> > features to have a clear and clean strategy instead of stacking features
> > on features, lacking coherency.
> > 
> > As stated by Regis, basing this work on top of SQLite may be the best
> > option, but more study has to be done and a general agreement is needed
> > to go this way.
> > 
> > Vincent
> > 
> >> Andreas
> >> 
> >> Am 23.05.2014 17:34, schrieb G. Allegri:
> >>> Recently I had to calculate the relative dimension of a polygon
> >>> relative to the others of the same class. I know there are a lot of
> >>> way to do it, inside and outside QGIS, but I wondered if field
> >>> calculator (and expressions in general) couls be extended to accompish
> >>> this kind of tasks.
> >>> 
> >>> The approach would be something similar WINDOW functions in 
Postgresql
> >>> [1], where for each record a new value will be calculated on the basis
> >>> of other records (filtered or not).
> >>> 
> >>> Has this ever been discussed? Is it something that could fit QGIS
> >>> expressions?
> >>> 
> >>> giovanni
> >>> 
> >>> [1] http://www.postgresql.org/docs/9.1/static/tutorial-window.html
> >>> 
> >>> 
> >>> 
> >>> _______________________________________________
> >>> Qgis-developer mailing list
> >>> Qgis-developer at lists.osgeo.org
> >>> http://lists.osgeo.org/mailman/listinfo/qgis-developer
> >> 
> >> _______________________________________________
> >> Qgis-developer mailing list
> >> Qgis-developer at lists.osgeo.org
> >> http://lists.osgeo.org/mailman/listinfo/qgis-developer
> 
> _______________________________________________
> Qgis-developer mailing list
> Qgis-developer at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/qgis-developer