title: INSERT Batch, and if duplicate key Update in codeigniter
body: <p>Is there any way of performing in batch Insert query and if the key already exists, UPDATE that row in codeigniter?
  I have gone through the documentation and found only insert_batch and update_batch. But how to update the row with duplicate key in active records? And what happens if one row fails to be inserted or updated in batch_insert? All insertion fails or only that row?</p>