title: MySQL group data by hour to get average
body: <pre><code>....  
  09.05.11 12:10 |    14,5  
  09.05.11 12:00 |    19,5  
  09.05.11 11:50 |    13,9  
  09.05.11 11:40 |    15,4  
  09.05.11 11:30 |    15,6  
  09.05.11 11:20 |    14,3  
  09.05.11 11:10 |    16,7  
  09.05.11 11:00 |    19,3  
  09.05.11 10:50 |    12,6  
  09.05.11 10:40 |    10,8  
  09.05.11 10:30 |    10,5  
  09.05.11 10:20 |    15,6  
  09.05.11 10:10 |    14,9  
  09.05.11 09:00 |    10,1  
  09.05.11 09:50 |    10,7  
  ....  
  </code></pre>
  
  <p>I need <code>AVG</code> data for every hour.</p>
  
  <p>ex. average data from <code>09.05.11 11.00</code> is calculated from  (<code>09.05.11 10.10</code> to <code>09.05.11 11.00</code>).</p>
  
  <p><code>12.00</code> from <code>11.10 - 12.00</code>  and so on...</p>
  
  <p>How can I do this?</p>