title: sql records in last few hours
body: <p>I have records in mysql table and I want to know how many records were in last 3, 7 and 12 hours. What would be the sql for that? My date field in in the format as</p>
  
  <pre><code>2010-08-09 09:52:27 
  2010-08-09 09:52:27 
  2010-08-09 09:52:27 
  2010-08-09 10:44:46 
  2010-08-09 10:44:46 
  2010-08-09 11:58:27 
  2010-08-09 14:48:22 
  2010-08-09 14:48:22 
  </code></pre>