title: Create table with calculated column
body: <p>I want to create table with three columns:</p>
  
  <pre><code>START_DATE|END_DATE|TOTAL_TIME 
  </code></pre>
  
  <p><code>START_DATE</code> and <code>END_DATE</code> should both be <code>date</code>s.
  <code>TOTAL_TIME</code> should be calculated by using these two columns. How can I create the table?</p>