Hi,
Yes, the use cases that triggered this project are:
* print composer
* atlas printing
* tables and forms (virtual fields): aggregates on related tables
(e.g. show all owners of a parcel, or the count or mean age of all trees
in a parcel)
Who knows, it could even be useful in labelling, symbology, etc. - e.g.
using the above example with the trees: color the parcels based on the
mean age of all trees in the parcels.
I guess there are many more use cases we don't even think about
currently.
Andreas
On 2016-03-16 09:21, Nyall Dawson wrote:
> On 16 March 2016 at 19:15, Hugo Mercier <[email protected]> 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.
>
> Nyall
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