Cassandra: The Definitive Guide, 3rd Edition

Chapter 4. The Cassandra Query Language

In this chapter, you’ll gain an understanding of Cassandra’s data model and how that data model is implemented by the Cassandra Query Language (CQL). We’ll show how CQL supports Cassandra’s design goals and look at some general behavior characteristics.

For developers and administrators coming from the relational world, the Cassandra data model can be difficult to understand initially. Some terms, such as keyspace, are completely new, and some, such as column, exist in both worlds but have slightly different meanings. The syntax of CQL is similar in many ways to SQL, but with some important differences. For those familiar with NoSQL technologies such as Dynamo or Bigtable, it can also be confusing, because although Cassandra may be based on those technologies, its own data model is significantly different.

So in this chapter, we start from relational database terminology and introduce Cassandra’s view of the world. Along the way you’ll get more familiar with CQL and learn how it implements this data model.

The Relational Data Model

In a relational database, the database itself is the outermost container that might correspond to a single application. The database contains tables. Tables have names and contain one or more columns, which also have names. When you add data to a table, you specify a value for every column defined; if you don’t have a value for a particular column, you use null. This new entry adds a row to the table, which you ...