title: Oracle, Make date time's first day of its month
body: <p>I have a datevariable, I would like to have convert it to first day of its monh,</p>
  
  <ul>
  <li>Eg: 10/10/2010 -> 01/10/2010  </li>
  <li>Eg: 31/07/2010 -> 01/07/2010  </li>
  </ul>