title: Can not calculate needed result
body: <p>I use MySql. I have tables :</p>
  
  <p>mails</p>
  
  <pre><code>id | user_id | date
  1      2       2012/08/21
  2      2       2012/08/22
  </code></pre>
  
  <p>calls  </p>
  
  <pre><code>id | user_id | date 
   1     2       2012/08/21
   2     2       2012/08/21
  </code></pre>
  
  <p>i want to get SUM of calls and mails for user for some date. e.g:</p>
  
  <pre><code>date       | SUM
  2012/08/21   3
  2012/08/22   1
  </code></pre>