title: How can I retrieve difference between two columns in time format?
body: <p>I have 2 columns called record time and unload time which are in time format "AM/PM" and I require a new column called total time to calculate difference between unload time and record time...</p>
  
  <p>For example here is my table:</p>
  
  <pre><code>record time                  unload time
  11:37:05 PM                  11:39:09 PM
  11:44:56 PM                    1:7:23 AM
  </code></pre>
  
  <p>I need a third column that contains the difference between these two columns.  It must be in the following format: "1:1:1"</p>
  
  <p>For the above example, I need the output:</p>
  
  <pre><code>record time                  unload time         total time
  11:37:05 PM                  11:39:09 PM         0:2:04
  11:44:56 PM                    1:7:23 AM         1:22:27
  </code></pre>
  
  <p>How would I write a query to achieve this?</p>