[Qgis-user] SQL display expression

[Christoph Lauber]

Hi

 

I have a question about the display expression for forms.  The aim is to
show data of a table that is not related by QGIS.

 

What I would like to do is to write a SQL to my SpatiaLite database to fetch
some data. I suppose, that the display expression is restricted to the
“select column” clause like: “"pkuid"   ||  ' '  || CASE WHEN art = 1 THEN
'this' ELSE 'that' END”. When I put a select clause in it like “CASE WHEN
"art" THEN (SELECT value FROM WI_D_Inventar_Art WHERE id = "art") ELSE
'Undefined' END” I get an expression is invalid error (the expression works
in spatialite_gui). It seems that the SELECT keyword is not accepted.

 

Is there any possibility to write “free” SQL-Syntax for the display
expression?

 

I wrote already a function that connects to the database, fetchs the data
and closes the database. It works, but it is slow.

 

Thanks for your help.

 

Freundliche Grüsse

Christoph Lauber

 

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