Hive dynamic partitioning

You need to modify your select:

set hive.exec.dynamic.partition=true;
INSERT OVERWRITE TABLE demo_tab PARTITION (land)
SELECT stadt, geograph_breite, id, t.country
FROM demo_stg t;

I am not sure to which column on your demo staging you want to perform partitioning or which column in demo corresponds to land. But whatever is the column it should be present as the last column in select say your demo table column name is id so your select should be written as:

INSERT OVERWRITE TABLE demo_tab PARTITION (land)
SELECT stadt, geograph_breite, id, t.country,t.id as land
FROM demo_stg t;

I think this should work.