title: Exclude Duplicate Objects in django queryset
body: <p>I have model called StudentAppeared</p>
  
  <pre><code>class StudentAppeared(models.Model):
      roll_number = models.CharField(max_length=50)
  </code></pre>
  
  <p>Assume i have following data</p>
  
  <p><img src="https://i.stack.imgur.com/zujc3.png" alt="enter image description here"></p>
  
  <p>From the above data result should display</p>
  
  <p><img src="https://i.stack.imgur.com/J75fF.png" alt="enter image description here"></p>
  
  <p>How can i achieve this thing using django query for <strong><em>StudentAppeared</em></strong> model?</p>