Book Image

Learning Apache Cassandra - Second Edition

Book Image

Learning Apache Cassandra - Second Edition

Overview of this book

Cassandra is a distributed database that stands out thanks to its robust feature set and intuitive interface, while providing high availability and scalability of a distributed data store. This book will introduce you to the rich feature set offered by Cassandra, and empower you to create and manage a highly scalable, performant and fault-tolerant database layer. The book starts by explaining the new features implemented in Cassandra 3.x and get you set up with Cassandra. Then you’ll walk through data modeling in Cassandra and the rich feature set available to design a flexible schema. Next you’ll learn to create tables with composite partition keys, collections and user-defined types and get to know different methods to avoid denormalization of data. You will then proceed to create user-defined functions and aggregates in Cassandra. Then, you will set up a multi node cluster and see how the dynamics of Cassandra change with it. Finally, you will implement some application-level optimizations using a Java client. By the end of this book, you'll be fully equipped to build powerful, scalable Cassandra database layers for your applications.
Table of Contents (14 chapters)

Adding columns to tables


Let's say we want to allow our users to enter their location in the profile. To store a user's location, we need a new column in the users table; fortunately, it's perfectly straightforward to add a new column to an existing table:

ALTER TABLE "users" ADD "city_state" text; 

This query instructs Cassandra that we'd like to add a column named city_state, of type text, to the users table. It's identical to the equivalent operation in SQL, although the CQL ALTER TABLE statement is much more constrained in the operations it can perform.

Now let's check our table schema again:

DESC TABLE "users";

Here, we have used the command DESC, which is a short version of the DESCRIBE command. As we hoped, we've got a city_state column in the schema. I've omitted the table properties for brevity: