[Qgis-user] geopackage spatial query

[Mithoefer]

Dear List,

I have a geopackage database and tried to use a spatial sql function 
(st_area) using the db manager in qgis 3.4  --> select st_area(geom) 
from polygon_filename. The function is available, but the result is 
Null. What is the problem?

Thanks a lot

Kind regards

Klaus