title: how does the groupby and count work in sql
body: <p>1> <code>select browser,count(*) from logtest group by browser;</code></p>
  
  <pre><code>+-----------+----------+
  | browser   | count(*) |
  +-----------+----------+
  | Firefox 3 |       14 |
  | Unknown   |       11 |
  +-----------+----------+
  </code></pre>
  
  <p>2 rows in set</p>
  
  <p>2> <code>select browser,count(browser) from logtest group by browser;</code></p>
  
  <pre><code>+-----------+----------------+
  | browser   | count(browser) |
  +-----------+----------------+
  | Firefox 3 |             14 |
  | Unknown   |             11 |
  +-----------+----------------+
  </code></pre>
  
  <p>2 rows in set</p>
  
  <p>3> <code>select browser,count(browser) from logtest;</code></p>
  
  <pre><code>+-----------+----------------+
  | browser   | count(browser) |
  +-----------+----------------+
  | Firefox 3 |             25 |
  +-----------+----------------+
  </code></pre>
  
  <p>1 row in set</p>
  
  <p>Why the query manner 1> and 2> result in the same result? Is there nothing difference between the count(*) and count(somefiled)?</p>
  
  <p>Also,whay the query 2> and 3> result in the different result,why the <strong>groupby</strong> so magic? How does it work?</p>
  
  <hr>
  
  <p>UPDATE:
  I am using MySQL5.1. :)</p>