title: Statistic : Compare previous value with actual value, database structure
body: <p>I'd like to be able to tell if the actual value is higher than the previous week (we take -7 calendar days). So i could show the information and its evolution :</p>
  
  <p><img src="https://i.stack.imgur.com/Km9Bt.png" alt="status"></p>
  
  <p>For that case i am talking about the status of my work item (post). This is my table (See status and status_last_update):</p>
  
  <p><img src="https://i.stack.imgur.com/9T5HW.png" alt="table"></p>
  
  <p>So to implement this new feature, i am thinking about 2 solutions. I'd like to know which one would be better and the reason for it. Or if there is any better solution.</p>
  
  <p>First solution : i add 2 more columns in my actual table "previous_status" "previous_status_last_update".</p>
  
  <p>Second solution : I create a new table that will store the previous status and the date of its last update.</p>
  
  <p>Third solution : I create a table storing the actual value and previous value :</p>
  
  <ul>
  <li>nb_new  </li>
  <li>nb_new_last_update </li>
  <li>nb_under_discussion </li>
  <li>nb_under_discussion_last_update </li>
  <li>nb_liked  </li>
  <li>nb_liked_last_update</li>
  <li>nb_disliked </li>
  <li>nb_disliked_last_update</li>
  <li>nb_approved</li>
  <li>nb_approved_last_update </li>
  <li>nb_rejected  </li>
  <li><p>nb_rejected_last_update</p></li>
  <li><p>nb_new_previous</p></li>
  <li>nb_new_last_update_previous</li>
  <li>nb_under_discussion_previous </li>
  <li>nb_under_discussion_last_update_previous</li>
  <li>nb_liked_previous </li>
  <li>nb_liked_last_update_previous </li>
  <li>nb_disliked_previous </li>
  <li>nb_disliked_last_update_previous </li>
  <li>nb_approved_previous</li>
  <li>nb_approved_last_update_previous </li>
  <li>nb_rejected_previous</li>
  <li>nb_rejected_last_update_previous</li>
  </ul>