title: SQL query to calculate sum of row with previous row
body: <p>This is my table </p>
  
  <pre><code>date     count of subscription per date
  ----      ----------------------------
  21-03-2016      10
  22-03-2016      30
  23-03-2016      40 
  </code></pre>
  
  <p>Please need your help, I need to get the result like below table, summation second row with first row, same thing for another rows:</p>
  
  <pre><code>date     count of subscription per date
  ----      ----------------------------
  21-03-2016      10
  22-03-2016      40
  23-03-2016      80 
  </code></pre>