title: CodeIgniter Update Batch with Multiple Index
body: <p>I'm having problem with active record Update Batch on CodeIgniter.</p>
  
  <p>On the documentation,</p>
  
  <pre><code>$this-&gt;db-&gt;update_batch('mytable', $data, 'title');
  </code></pre>
  
  <p>Where 'title' is the index for the update process. Is it possible to have two or more index to this active record?
  I already tried</p>
  
  <pre><code>$this-&gt;db-&gt;update_batch('mytable', $data, 'title, title_2');
  $this-&gt;db-&gt;update_batch('mytable', $data, array('title', 'title_2');
  </code></pre>
  
  <p>And it's not working.</p>