title: Update Batch in Codeigniter with multiple WHERE clause
body: <p>I checked the CI user guide to see how to handle <code>update_batch()</code> and it seems it accept onlt one index to match which row to be updated.</p>
  
  <p>But in my instance, i need to specify two index like <code>lang</code> and <code>id_page</code> which i use as index together. such <code>lang=en|id_page=115</code> is unique so the key for the row.</p>
  
  <p>Means, my where index should be <code>WHERE lang = $lang AND id_page = $id_page</code> ...</p>
  
  <p>Is there any approach on batch update with multiple index?</p>
  
  <p>Thank you.</p>