I have a shapefile to which I've joined a table, matching with an ID field. All the fields of the table show up correctly when I open the shapefile's attribute table. But when I go into vector/analysis tools/basic statistics I can only choose one of the fields in the shapefile itself; those I have joined are missing.
I've noticed joining fields in QGIS is limited in that if you want to make use of those newly added fields, for example in any query for sub-setting or in further geoprocessing/analysis workflows, the join usually has to be made permanent.
Because you're working with shapefiles, a new dataset might have to be created.
- Join the data to your shapefile
- Export the shapefile (right click and "Save As...") to a new file that can be used for what you need because the joined data is now part of the dataset