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

Hugo Mercier hugo.mercier at oslandia.com
Wed May 28 08:05:18 PDT 2014

Le 27/05/2014 15:03, Régis Haubourg a écrit :
> Hugo Mercier wrote
>> Or
>>> calculated fields in view can't be explicitly cast, so QGIS should have
>>> to
>>> guess data type based on a data scan (a major unadressed issue of sqlite)
>> Hmmm I wasn't aware of this limitation in SQLITE views :(
> Yes, SQLITE does dynamic typing, so user or provider has to scan values to
> guess the right type. 
> Here is a sqlite topic on that [0]
> And here my initial post in qgis list [1]
> [0]
> http://sqlite.1065341.n5.nabble.com/Computed-columns-in-VIEWs-return-NULL-but-should-be-able-to-be-typed-Any-ideas-td56769.html#a56770
> [1]
> http://osgeo-org.1560.x6.nabble.com/Spatialite-can-t-type-fields-of-a-view-td5058436.html

Still on this topic. I made a few tests with sqlite views.
Indeed you cannot enforce a particular column type, but :
* you can convert values with CAST (casting 'foobar' to integer gives
0), even if the resulting type is undefined
* QGIS does not seem to have any particular problem with untyped SQLite
columns, they will be reported as TEXT (QString) in the layer properties
* Even if the column is untyped, each value has its own type. So if a
column results from a CAST, to integer say, then the corresponding
attribute will be in a QVariant typed as an integer when it is fetched.
You can then use this value in a QgsExpression or a categorized
symbology as an integer.

Am I missing other use cases where not having a column type is a problem ?

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