title: how to get the count showing up iper week
body: <p>The table shows the car plate number, showing time, location of cameras. I need to find the cars who show up in every week for more than once, I need to know who are they and the showing frequency for each week, and the total number of the cars that fulfill the conditions. </p>
  
  <p>I tried to split the time period manually, but that's too inefficient.
  I tried the following query:</p>
  
  <pre><code>   SELECT *, 
         Variance(Time_to_sec(time)), 
         Count(*) 
     FROM   trafficdata.anpr_in 
     WHERE  location = 'a35.1.ob.1' 
         AND Date(time) BETWEEN '2012-05-09'AND '2012-05-15' 
         AND Time(time) BETWEEN '07:00:00' AND '07:05:00' 
     GROUP  BY plate 
     HAVING ( Count(plate) &gt; 3 ); 
  </code></pre>
  
  <p>The input table looks like:</p>
  
  <pre><code>  plate         location     number                    time
  T971JUR     A3024.7.IB.1         96     2012-05-13 18:06:17
  HN52YWE     A3024.13.OB.1        94     2012-05-13 18:09:53
  </code></pre>