title: Query cache in yii
body: <p>If I want to use Query Caching as in the tutorial here :</p>
  
  <p><a href="http://www.yiiframework.com/doc/guide/1.1/en/caching.data" rel="nofollow">Yii Query Caching Guide</a></p>
  
  <p>whether I should have a <strong>update_time</strong> field in every table?</p>
  
  <pre><code>$dependency = new CDbCacheDependency('SELECT MAX(update_time) FROM tbl_post');
  </code></pre>
  
  <p>Is the field must exist to be able to use the query cache?</p>