title: About DatePart in Date functions
body: <p>I couldn't understand the difference between</p>
  
  <pre><code>SELECT DATEDIFF(D,'07/09/1978',GETDATE())
  
  SELECT DATEDIFF(DD,'07/09/1978',GETDATE())
  </code></pre>
  
  <p>Both are giving the same value. Then what is the difference between D, and DD?</p>
  
  <p>I have the same question for</p>
  
  <ul>
  <li><code>M, MM</code></li>
  <li><code>Q, QQ</code></li>
  <li><code>YY, YYYY</code> </li>
  </ul>
  
  <p>Can anybody please explain this to me?</p>