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)

Updating the existing rows


Now that we've got a new location column, we can add some data to it. Any new user records we create, of course, can have a location value, but perhaps some of our existing users would like to input their location value too. To do this, we need to be able to update existing rows. The process should, once again, look quite familiar to anyone who is familiar with SQL:

UPDATE "users" 
SET "location" = 'New York, NY' 
WHERE "username" = 'alice';

Like the INSERT and DELETE statements, the UPDATE statement does not give us any feedback on the operation. However, we can confirm whether it worked by reading from the users table again:

SELECT * FROM "users"; 

As we hoped, alice now has a location:

Note

A full reference for the UPDATE statement can be found in the DataStax CQL documentation at http://www.datastax.com/documentation/cql/3.3/cql/cql_reference/update_r.html.

Updating multiple columns

As in the SQL UPDATE statement, we can specify multiple column-value pairs to be updated...