In this chapter, we were introduced to the concept of compound primary keys, and learned that a primary key consists of one or more partition keys and, optionally, one or more clustering columns. We saw how partition keys—the only type of key we had previously encountered—can group related rows together, and how clustering columns provide an order for these rows within each partition.

Compound primary keys allow us to build a table containing users' status updates because they expose two important structures: grouping of related rows, and ordering of rows. In the user_status_updates table, we encoded the relationship between users and their status updates implicitly in the structure of the primary key; the partition key refers to the parent row in the users table. We also explored the use of static columns to make this relationship explicit, storing all the information about users and their status updates in a single table.

In Chapter 4, Beyond Key-Value Lookup, we will dive into new...