title: what is the same equivalent query in `rails console` with this sql ?
body: <p>SQL:</p>
  
  <pre><code>select * from user where room_id not in (select id from rooms);
  </code></pre>
  
  <p>what is the same equivalent query in <code>rails console</code>  with this sql? </p>
  
  <p>ex:</p>
  
  <pre><code>User.all.each { |u| user.room }
  </code></pre>
  
  <p>(sorry, but this example is not correct.)</p>