Running Cassandra 3.0.2
Using the official example from:
The only difference is that I have added a map column to the base table.
All of the above works perfectly fine. Until you insert a row where the 'a_map' column is not null.
This results in:
Selecting the base table and the materialised view is also interesting:
The result is:
In the logs you can see:
As the logs say, ColumnDefinition 'a_map' is not a subset of  (which is all non-primary key columns of the materialised view. There are no such column in this example).
And if you drop this materialised view and create a new one where the 'a_map' is being selected, it all works.
Is this a documented limitation or a bug? I was trying to find a documentation that says "all collection columns must be selected in a materialised view", but I could not find such a thing. I tested it with sets in addition to maps and it is pretty much the same.