I use a Swiss shape file map (called PLZO_PLZ) available on http://www.cadastre.ch/internet/cadastre/fr/home/products/plz/data.html (ZIP file Shape LV03)
PLZO_PLZ contains a column called PLZ which correspond to a swiss locality. For instance number PLZ 1202 is in Geneva. By the way, PLZ can also be called NPA (same meaning).
My aim is to get a colored map according to the NPA frequency coming from an external CSV file: http://pastebin.com/raw.php?i=iAjV88KQ
For instance NPA not appearing in the CSV should be not colored (white) and NPA coming few time should appear in light blue and the more frequent the NPA is the more dark blue should be the map. According to my CSV NPA 1203 should be the darkest.
Is it possible to obtain what I am looking for with Quantum GIS? (I tried to use "Joins" function in proprieties but it's not working)
Edit: I try to join like this :