title: Check if data exists in Django annotate queryset
body: <p><em><strong>Environments</strong></em></p>
  <ul>
  <li>Django 2.0</li>
  <li>DRF 3.11</li>
  <li>mariaDB</li>
  </ul>
  <p>I want to output'N' if at least one of the columns is 0, and'Y' if all of them are 1.</p>
  <hr />
  <p><em><strong>Database</strong></em>
  <a href="https://i.stack.imgur.com/Dp4ld.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Dp4ld.png" alt="database example" /></a></p>
  <hr />
  <p><em><strong>Model</strong></em></p>
  <pre class="lang-py prettyprint-override"><code>class UserPoint:
      user = models.ForeignKey('User', others options)
      poinit = models.IntegerField()
      used = models.SmallIntegerField(default=0)
      deleted = models.SmallIntegerField(default=0)
  </code></pre>
  <hr />
  <p><em><strong>Expected results</strong></em></p>
  <ul>
  <li>total_point_used : Sum of points where used is 1</li>
  <li>used_status : 'N' if any of used has 0 or 'Y' if all values ​​of used are 1</li>
  </ul>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>user</th>
  <th>username</th>
  <th>total_point_used</th>
  <th>used_status</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>1</td>
  <td>'AA'</td>
  <td>600</td>
  <td>'N'</td>
  </tr>
  <tr>
  <td>2</td>
  <td>'BB'</td>
  <td>0</td>
  <td>'N'</td>
  </tr>
  <tr>
  <td>3</td>
  <td>'CC'</td>
  <td>500</td>
  <td>'Y'</td>
  </tr>
  </tbody>
  </table>
  </div><hr />
  <p><em><strong>Tried queryset</strong></em></p>
  <pre class="lang-py prettyprint-override"><code>q = UserPoint.objects.filter(
      deleted=0
  ).values(
  
      username=F('user__username')
      .... others values ....
  
  ).annotate(
      
      total_point_used=Sum(  # Sum of used point
                  Case(
                      When(
                          used=1,
                          then='point',
                      ), output_field=IntegerField(),
                  )
              ),
  
      # I don't know what to do with used_status.
      # tried &lt;- not work
      #used_status=Case(
      #                When(
      #                    used=1,
      #                    then=Value('Y')
      #                ),
      #            default=Value('N'),
      #            output_field=CharField()
      #        )
  
      # I want something like this.
      used_status=Exists(used=0, then='N', default='Y')
  )
  </code></pre>
  <hr />
  <p>How can I get the value I expect in annotate?</p>