[Qgis-developer] have aggregate/window expressions ever been discussed?
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
>>> calculated fields in view can't be explicitly cast, so QGIS should have
>>> 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 
> And here my initial post in qgis list 
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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