title: using subquery instead of the tablename
body: <pre><code>Table Meta:
  -------------------------------------
  type                  tab_name
  new                   tab_news
  sports                tab_sps
  
  Table tab_news
  ------
  id
  
  Table tab_sps
  -------------------
  id
  xx
  </code></pre>
  
  <p>Now I want to use </p>
  
  <pre><code>SELECT id 
    FROM (SELECT tab_name 
            FROM Meta 
           WHERE type = 'news');
  </code></pre>
  
  <p>But it does not work, any ideas?</p>