title: Modelling Unique constraints in Cassandra
body: <p>I am a newbie to Cassandra. I would like to know how to model a unique constraint scenario in Cassandra.</p>
  
  <p>E.g. I have a users table with the columns username, email, First Name.
  Since no 2 users should be allowed to have the same username nor should they be allowed to have the same email id, how do I model this?</p>
  
  <p>In traditional RDMS terms, I would create Unique Keys on each of the columns.</p>
  
  <p>Thanks</p>