title: count columns group by
body: <p>
  I hava the sql as below:
  </p>
  
  <pre><code>select a.dept, a.name
    from students a
   group by dept, name
   order by dept, name
  </code></pre>
  
  <p>And get the result: </p>
  
  <pre><code>dept   name
  -----+---------
  CS   | Aarthi
  CS   | Hansan
  EE   | S.F
  EE   | Nikke2
  </code></pre>
  
  <p>I want to summary the num of students for each dept as below:</p>
  
  <pre><code>dept   name        count
  -----+-----------+------  
  CS   | Aarthi    |  2
  CS   | Hansan    |  2
  EE   | S.F       |  2
  EE   | Nikke2    |  2
  Math | Joel      |  1
  </code></pre>
  
  <p>How shall I to write the sql?</p>