title: Codeigniter method for update
body: <pre><code>$age=10;
  $id=1;
  $sql='update student set age=age+$age where sid=$id;
  </code></pre>
  
  <p>I want to write this sql statement using Codeigniter how is that possible?Any native way in Codeigniter to do this? I am using Codeigniter active record</p>