Can a primary key in Cassandra contain a collection column?

Question

Can a primary key in Cassandra contain a collection column?

Example:

CREATE TABLE person (
  first_name text,
  emails set<text>,
  description text

  PRIMARY KEY (first_name, emails)
);

Answer 1

I'd say no: because the collection is mutable, and you can't have a primary key that keeps changing in time.

Answer 2

It's been a while but as this is on first page in Google when you look for using a map in the primary key, I thought it was worth to update it.

Cassandra now allows (I think since 2.1) to use a collection in a Primary Key provided it is frozen.

A frozen value serializes multiple components into a single value. Non-frozen types allow updates to individual fields. Cassandra treats the value of a frozen type as a blob. The entire value must be overwritten.

With frozen, the collection becomes essentially immutable not allowing for modifications in-place, therefore, becoming suitable for a Primary Key.

Here is an example using a frozen list.

CREATE TABLE test_frozen (
    app_id varchar,
    kind varchar,
    properties frozen <list<text>>,
    PRIMARY KEY ((app_id, kind), properties));

Since 2.1, Cassandra also allows to create an index on columns of type map, set or list - though that not's necessarily a good idea.