Re: [Qgis-developer] Aggregates within expression engine

Hi, Hi, I remember having had such a discussion with Hugo and matthias when choosing what could be the best way for doing aggregates and relational queries in QGIS. At that time, we chose to test virtual layers path because all database query planner stuff seemed too much work to recode in QGIS

Re: [Qgis-developer] Aggregates within expression engine

> > So, thoughts and feedback welcome, no matter how off-the-cuff they are! ;) > > Nyall > Given that using SQL is maybe "harder", and that Mr. Paolo also have a good point aiming to ease to use: i would like just to remind what the very nature of a G.I.S. is, namely a Database, usually with

Re: [Qgis-developer] Aggregates within expression engine

+1 Luigi Pirelli ** * Boundless QGIS Support/Development: lpirelli AT boundlessgeo DOT com * LinkedIn: https://www.linkedin.com/in/luigipirelli * Stackexchange:

Re: [Qgis-developer] Aggregates within expression engine

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

Re: [Qgis-developer] Aggregates within expression engine

On 16/03/2016 09:21, Nyall Dawson wrote: > On 16 March 2016 at 19:15, Hugo Mercier 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

Re: [Qgis-developer] Aggregates within expression engine

On 16 March 2016 at 19:15, Hugo Mercier 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

Re: [Qgis-developer] Aggregates within expression engine

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

Re: [Qgis-developer] Aggregates within expression engine

Hi Paolo On 03/16/2016 09:08 AM, Paolo Cavallini wrote: > Hi Matthias, > > Il 16/03/2016 08:47, Matthias Kuhn ha scritto: > >> Sorry, I'm not familiar with the spreadsheet syntax. Can you make some >> examples so we can compare the advantages and drawbacks in detail? > > best if you have a

Re: [Qgis-developer] Aggregates within expression engine

Hi Matthias, Il 16/03/2016 08:47, Matthias Kuhn ha scritto: > Sorry, I'm not familiar with the spreadsheet syntax. Can you make some > examples so we can compare the advantages and drawbacks in detail? best if you have a look to LibreOffice help itself. BTW, we already used the LO help for the

Re: [Qgis-developer] Aggregates within expression engine

Il 16/03/2016 08:53, Neumann, Andreas ha scritto: > And what would be the alternative syntax that is easier than SQL syntax? as said, everyone knows at least some spreadsheet syntax > Please try to be more specific rather than just saying SQL syntax is > complicated. I'm not saying it is

Re: [Qgis-developer] Aggregates within expression engine

On Wed, Mar 16, 2016 at 6:17 AM, Nyall Dawson wrote: > I'm also torn regarding the best syntax to use for aggregates within > expressions. I'm unsure if the traditional SQL "group by" clauses > would be a good fit within the existing QGIS expression syntax (eg >

Re: [Qgis-developer] Aggregates within expression engine

Hi, just my 2 ct: I agree with Paolo that normal users do not know SQL, on the other hand there might be users that do not know spreadsheet syntax either (e.g. me :) which spreadsheet BTW: Excel? LO? or do they use the same syntax? SQL would be a standardized approach (and is the syntax

Re: [Qgis-developer] Aggregates within expression engine

Hi Paolo, And what would be the alternative syntax that is easier than SQL syntax? Please try to be more specific rather than just saying SQL syntax is complicated. Syntax that allows to use aggregate functions and grouping for the following use cases: Aggregate functions: All data types:

Re: [Qgis-developer] Aggregates within expression engine

Hi Paolo, On 03/16/2016 08:36 AM, Paolo Cavallini wrote: > Il 16/03/2016 08:30, Neumann, Andreas ha scritto: > >> Why do you think SQL aggregate syntax (e.g. as outlined >> at http://www.postgresql.org/docs/9.5/interactive/functions-aggregate.html) >> is a no-go? Can you explain this in detail?

Re: [Qgis-developer] Aggregates within expression engine

Il 16/03/2016 08:30, Neumann, Andreas ha scritto: > Why do you think SQL aggregate syntax (e.g. as outlined > at http://www.postgresql.org/docs/9.5/interactive/functions-aggregate.html) > is a no-go? Can you explain this in detail? QGIS is much closer to a > database then it is to a spreadsheet -

Re: [Qgis-developer] Aggregates within expression engine

Hi Paolo, Thank you for your feedback. Why do you think SQL aggregate syntax (e.g. as outlined at http://www.postgresql.org/docs/9.5/interactive/functions-aggregate.html) is a no-go? Can you explain this in detail? QGIS is much closer to a database then it is to a spreadsheet - in fact for

Re: [Qgis-developer] Aggregates within expression engine

Hi Nyall, Il 16/03/2016 07:17, Nyall Dawson ha scritto: > I'm also torn regarding the best syntax to use for aggregates within > expressions. I'm unsure if the traditional SQL "group by" clauses > would be a good fit within the existing QGIS expression syntax (eg > "sum("some_field") group by

[Qgis-developer] Aggregates within expression engine

This has been discussed a few times in the past, but a possible funding opportunity has arisen and I'd like to get things moving on implementing this for 2.16. Before I start a QEP I thought an informal discussion concerning the approach is a good idea. My thoughts are: - Calculation of