title: Sum up Time column using sql query
body: <p>I have a table as follows</p>
  
  <pre><code>repID   ClockIn     ClockOut    TotalHours
  109145  7:50:50 AM  3:37:16 PM  7:46:26
  109145  7:52:41 AM  3:44:51 PM  7:52:10
  109145  8:42:40 AM  3:46:29 PM  7:3:49
  109145  7:50:52 AM  3:42:59 PM  7:52:7
  109145  8:09:23 AM  3:36:55 PM  7:27:32
  </code></pre>
  
  <p>Here '<code>TotalHours</code>' column is obtained as diff of ClockIn and ClockOut</p>
  
  <p>Now I need to add all the data in column '<code>TotalHours</code>' Whose datatype in (<code>varchar</code>).</p>
  
  <p>How should I add this column.....</p>
  
  <p>I tried as</p>
  
  <pre><code>select SUM(TotalHours)
  </code></pre>
  
  <p>But it returns an error:</p>
  
  <blockquote>
    <p>Operand data type varchar is invalid for sum operator</p>
  </blockquote>
  
  <p>I also tried with casting it into <code>float</code>, <code>datetime</code> and <code>time</code>... </p>
  
  <p>But all returns error...</p>
  
  <p>Please help to sum up the time column....</p>