title: DynamoDB - Global Secondary Index on set items
body: <p>I have a dynamo table with the following attributes : </p>
  
  <ul>
  <li>id (Number - primary key )</li>
  <li>title (String)</li>
  <li>created_at (Number - long)</li>
  <li>tags (StringSet - contains a set of tags say android, ios, etc.,)</li>
  </ul>
  
  <p>I want to be able to query by tags - <em>get me all the items tagged android</em>. How can I do that in DynamoDB? It appears that global secondary index can be built only on ScalarDataTypes (which is Number and String) and not on items inside a set.</p>
  
  <p>If the approach I am taking is wrong, an alternative way for doing it either by creating different tables or changing the attributes is also fine.</p>