if I do select * from cf where primary_key='something' it returns 'something' even there is no rows. The CF was just created and it didn't exist before.
CQL (possible bug)(2 posts) (2 voices)
This is standard Cassandra behavior for now. It's important to understand that there is no concept of row existence in Cassandra apart from "does a row have columns or not". So a row with no columns should always be treated the same as an empty row.
If this behavior changes (which it probably will; the current situation is not intuitive), it will probably be under https://issues.apache.org/jira/browse/CASSANDRA-3505 .