title: Magento sort collection with multiple attributes
body: <p>I want to sort Magento product collection  with multiple attributes at catalog product list page. I am using this code </p>
  
  <pre><code>$this-&gt;_collection-&gt;setOrder('price', 'desc');
  $this-&gt;_collection-&gt;setOrder('price_plus_shipping', 'desc');
  </code></pre>
  
  <p>I also tried this code as well</p>
  
  <pre><code>$this-&gt;_collection-&gt;setOrder(array('price', 'price_plus_shipping'),Varien_Data_Collection::SORT_ORDER_DESC);
  </code></pre>
  
  <p>When i sort these both combine its not giving me accurate results but if i use both separately like when i am using only </p>
  
  <blockquote>
    <p>price_plus_shipping</p>
  </blockquote>
  
  <p>its working fine also as </p>
  
  <blockquote>
    <p>price</p>
  </blockquote>
  
  <p>its also working file 
  they are showing me accurate results. But i want to use them combine.
  in <strong>Price</strong> i have product prices in <strong>price_plus_shipping</strong> i have alphabets like </p>
  
  <blockquote>
    <p>a,b,c etc</p>
  </blockquote>