title: IFNULL Function is Not Working in MySQL Query
body: <p>I want operator by Grand Total. but <code>IFNULL</code> function is not working.</p>
  
  <pre><code>SELECT 
        IFNULL(op.operator_name, "Grand Total") AS operator, 
        SUM(re.amount) AS amount 
  FROM mobile_db.recharge re 
  INNER JOIN mobile_db.operator op 
  ON re.operator_id = op.operator_id
  GROUP BY operator WITH ROLLUP
  </code></pre>