To be specific, I have a shapefile on census block groups (CBGs) in Georgia, but I only want to use those in Atlanta's commuting zone (CZ).
However, commuting zone is not a field in the census shapefile, so I join the layer with a different table that links CBG IDs to CZs. If I want to filter this layer, I am prompted to define a virtual layer, which I duly do.
Yet when I save that virtual layer (showing all the original fields, and CZ, and only for CZ=141, which is Atlanta) the shapefile is empty, thus the geography is lost somewhere along the line.
What is the proper way to do this?
I am on QGIS 2.18.2.