title: Add case when statement in Yii SQL command object
body: <p>In YII, I have a already working function: </p>
  
  <pre><code>$sql = Yii::app()-&gt;db-&gt;createCommand();
  $sql-&gt;select('A.name as client_name, B.name as product_name');
  $sql-&gt;join('tableb B', 'A.id=B.product_id');
  $sql-&gt;from('tablea A');
  $sql-&gt;where('1 = 1');
  </code></pre>
  
  <p>Now I am trying to add a tiny logic to the product_name field, in MYSQL it would be </p>
  
  <pre><code>CASE WHEN B.name = "sth"
  THEN B.name 
  ELSE B.another_name
  END AS product_name
  </code></pre>
  
  <p>Is it possible to add this <strong>case when</strong> block in the select() function? </p>