title: Group and update multiple records sql based on another table
body: <p>I am stuck trying to figure out a way to execute an update over an entire table on field 'Factor'. </p>
  
  <p>'Factor' is determined by the number of repeated records with the same 'location' and 'date'.</p>
  
  <p>There is a factor calculation table:</p>
  
  <pre><code>Location - Count - Factor
     X     -   1    -   1.0
     X     -   2    -   0.8
     X     -   3+    -  0.5
  </code></pre>
  
  <p>Please help me out!</p>