title: How to do a group by on a concatenated Field?
body: <p>Say I have  a table for students attending school like this:</p>
  
  <pre><code>St_ID |St_Name|Class_ID|Year
  ------+-------+--------+----
   02345|John   |     345|2011
   07871|Jane   |     234|2010
  </code></pre>
  
  <p>and so on.
  I wish to run queries on each Class which I can get by concatenating Class_ID &amp; Year.
  i.e 345-2011 is one class</p>
  
  <p>How do I do count(*), by having the concatenated string in the Group by query?</p>