title: Count consecutive dates in SQL as one instance
body: <p>I would like to do a date count but count consecutive dates as one instance. In the example table below, <code>09/28/2013</code> and <code>09/29/2013</code> are consecutive therefore they count as one instance.</p>
  
  <pre><code>user_id      date   
  ------       ------ 
  ABC123       09/28/2013
  ABC123       09/29/2013
  ABC123       09/30/2013
  ABC123       10/01/2013
  </code></pre>
  
  <p><strong>Output:</strong></p>
  
  <pre><code>user_id      date_count   
  ------       ------ 
  ABC123       3
  </code></pre>