title: Python: DISTINCT on GQuery result set (GQL, GAE)
body: <p>Imagine you got an entity in the Google App Engine datastore, storing links for anonymous users. 
  You would like to perform the following SQL query, which is not supported:</p>
  
  <pre><code>SELECT DISTINCT user_hash FROM links
  </code></pre>
  
  <p>Instead you could use:</p>
  
  <pre><code>user = db.GqlQuery("SELECT user_hash FROM links")
  </code></pre>
  
  <p>How to use Python <strong>most efficiently</strong> to filter the result, so it returns a DISTINCT result set?
  How to count the DISTINCT result set?</p>