title: pseudo columns & DUAL table - what do they actually mean?
body: <p>Dual table is used to select pseudo columns.
  it has one row and one column DUMMY which has a value X.</p>
  
  <p>I have two questions </p>
  
  <ol>
  <li>What actually does a pseudo
  column mean?</li>
  <li><p>How is the dual able to give the
  value for example:</p>
  
  <pre><code>select sysdate from dual
  </code></pre>
  
  <p>will result in current datetime.  How is this possible?</p></li>
  </ol>