title: To sum the two non numeric columns
body: <p>Am using oracle 12c. I have 4 columns:</p>
  
  <pre><code>country   student_id (primary)  start_level     end_level
  -------   --------------------  -----------     ---------
  India     I20                   L3              L12
  India     I21                   L5              L9
  China     c10                   L4              L11
  USA       U20                   L2              L9
  Canada    C20                   L9              L12
  </code></pre>
  
  <p>From the above table structure I want to group by country wise total students with sum of levels.  For example the output like below:</p>
  
  <pre><code>Country|  Total_students| Total_levels
  India                  2            15
  </code></pre>
  
  <p>(Total level calculation : L3 to L12=10 + L5 to L9 =5. So, total levels 15)</p>
  
  <p>Can I use substr to find the level values or whatever is best?</p>