Looking up follow relationships

Now that we've studiously designed our follow tables to efficiently support our application's data access patterns, let's do some data access. To start, we'll want to give alice an interface to manage the list of users she follows; this interface will, of course, need to show her who she currently follows:

  SELECT "followed_username" 
  FROM "user_outbound_follows" 
  WHERE "follower_username" = 'alice';

Here, we ask for all of the outbound follows in the partition of alice: an efficient query since it only looks up a single partition's worth of data. As expected, we see that alice follows bob and carol:

Note that the usernames returned are in alphabetical order: this is not a coincidence. Since followed_username is the clustering column in the user_outbound_follows table, the rows are stored in string order of the...