The third and final collection type offered by Cassandra is the map, which stores key-value pairs. Keys are unique and unordered, like the elements of a set.
Suppose we'd like to keep track of our users' identities on other social networks. We could create a column for each network, but that would require changing the schema each time we discovered a new network that we want to track, and would also potentially result in a large number of columns in the users table just to keep track of a given user's identity.
Instead, let's create a map column that maps the name of a social network to the numeric ID of the user on that network:
ALTER TABLE "users" ADD social_identities MAP<text,bigint>;
This definition ...
