Execute 'SET a = b' query

I want to execute 'SET a = b' query using Active Record开发者_开发问答 in Codeigniter. I am using MySQL. I tried with

$this->db->set('a', 'b', FALSE);

But it executes

SET a = NULL

I think you can do:

$this->db->query('SET a = b')

Reference: http://codeigniter.com/user_guide/database/queries.html

• Christian