[Qgis-developer] Aggregates within expression engine

[Hugo Mercier]

On 16/03/2016 09:21, Nyall Dawson wrote:
> On 16 March 2016 at 19:15, Hugo Mercier <hugo.mercier at oslandia.com> wrote:
>> Hi,
>>
>> Just for me to understand: why not considering improving a bit the
>> virtual layers ?
>>
>> There is already a support for user defined aggregate functions. Caching
>> of the computed aggregate is already done by the engine (I guess). And
>> we could add some functions to restrict the query to the selected
>> features of a layer or deal with relations ...
>>
>> And using something like the "query builder" found in db manager (and
>> inspired by mapinfo), it may ease to deal with the SQL syntax ...
> 
> I think the use case is quite different. Having aggregates in
> expressions is useful for things like embedding the values in
> composers and atlas prints, or in data defined overrides.
> 

Sure, but "extending" a layer by a virtual layer that adds new columns
computed by aggregate functions could also be a solution.