Building an autocomplete function

So far, we've been focused on storing users and their status updates, but we can use our knowledge of compound primary keys to make it a bit easier to write status updates too. Let's introduce a hashtagging function into the status update composition interface and then autocomplete hashtags as users type them.

First, we'll set up a table to store hashtags using the following query:

CREATE TABLE "hash_tags" ( "prefix" text, "remaining" text, "tag" text, PRIMARY KEY ("prefix", "remaining"));

The structure of our table is a bit unusual, but it will work very well for our purposes. The partition key is a prefix, which we'll use to store the first two letters of each hashtag. The clustering column, remaining, will store the remaining letters of the hashtag, and tag will contain the entire hashtag start to finish.

By partitioning the table this way, we'll make things easy for Cassandra by immediately narrowing down the list of possible autocomplete tags to those in...