title: How to sum value of all Key in Redis
body: <p>In Redis DB, i have many key in String type to save dowloads time with a application, 
  example: </p>
  
  <pre><code>   Key            value
  20131028:1         100
  20131028:2         15
  20131028:3         10
  ..........
  </code></pre>
  
  <p>I want to sum all value of all key by redis command, please helpe me solve it. Thank you so much.</p>