title: populate a column based on current row and previous row's value mysql
body: <p>I have a table <code>tb1</code> like this：</p>
  
  <pre><code>ID      DATE_     STATs 
  1      2007-01     0.2
  1      2007-02     0.12
  1      2007-03     0.42
  1      2007-04     0.23
  1      2007-05     0.26
  1      2007-06     0.17
  2      2007-01     0.33
  2      2007-02     0.14
  2      2007-03     0.21
  2      2007-04     0.35
  2      2007-05     0.67
  2      2007-06     0.07
  </code></pre>
  
  <p>How do I add an additional column computed by: </p>
  
  <pre><code>(1+current.STATs) / (1+priorMonth.STATs) - 1
  </code></pre>
  
  <p>for each ID?</p>