Hope that helps The primary keys directly determine how and where cassandra stores the data contained in a table (column family). The primary key consists of partition key and clustering key (optional).
Why can't I add WHERE clauses in Cassandra after filtering on the primary key?
this will help No, an index is not automatically created on the clustering column of a composite key. If you created a secondary index on the clustering column you would actually suffer a performance hit when querying by it. Secondary indexes in Cassandra exist for convenience, not for performance. The bottom line is that they don't scale well, and a single query usually ends up having to hit several nodes in your cluster.
Cannot define PRIMARY KEY Constraint on nullable column when column is already NOT NULL