title: difference between count(*) and count(columnName)
body: <p>I would like to know what are the differences between using:</p>
  
  <pre><code>SELECT email, COUNT( email ) AS total
  FROM `newsletter`
  GROUP BY email having total&gt;1
  </code></pre>
  
  <p>or</p>
  
  <pre><code>SELECT count(*) as total, email 
  FROM 'newsletter' 
  GROUP BY email having total &gt; 1
  </code></pre>
  
  <p>Both give same results but what else is counting <code>count(*)</code> than the emails?</p>