title: Magento 1.7.0.2 Filter by multiple categories - SQL Error
body: <p>Refering to
  <a href="https://stackoverflow.com/questions/12498556/magento-1-7-filter-products-by-multiple-categories">Magento 1.7 Filter products by multiple categories</a>
  I have a new question:</p>
  
  <p>I'am using Magento 1.7.0.2 and the described solutions to filter a product-collection by multiple categories (via AND) does not work for me.</p>
  
  <p>My categorie structure:</p>
  
  <ul>
  <li>Root
  
  <ul>
  <li>cat 1
  
  <ul>
  <li>cat 1a</li>
  <li>cat 1b</li>
  </ul></li>
  <li>cat 2
  
  <ul>
  <li>cat 2a</li>
  <li>cat 2b</li>
  </ul></li>
  <li>cat 3</li>
  </ul></li>
  </ul>
  
  <p>A product for example can be in cat 1a, cat 2 and cat 2b at the same time.
  It should be listed, if I filter:</p>
  
  <ul>
  <li>after cat 1a</li>
  <li>after cat 1a &amp; cat 2</li>
  <li>after cat 1a &amp; 2b &amp; 2</li>
  </ul>
  
  <p>It must <strong>not</strong> be visible, if I filter:</p>
  
  <ul>
  <li>after cat 3</li>
  <li>after cat 1 &amp; cat 1a</li>
  <li>after cat 1a &amp; 2a</li>
  </ul>
  
  <p>My Code:</p>
  
  <pre><code>$_productCollection = Mage::getModel('catalog/product')
          -&gt;getCollection()
          -&gt;joinField('category_id', 'catalog/category_product', 'category_id', 'product_id = entity_id', null, 'left')
          -&gt;addAttributeToSelect('*')
          -&gt;addAttributeToFilter('category_id',
              array("finset" =&gt; array(53, 46))
          );
  </code></pre>
  
  <p>This gets me a SQL-Error:</p>
  
  <pre><code>#1582 - Incorrect parameter count in the call to native function 'FIND_IN_SET'
  SELECT `e`.*, `at_category_id`.`category_id` FROM `catalog_product_entity` AS `e`
  LEFT JOIN `catalog_category_product` AS `at_category_id` ON (at_category_id.`product_id`=e.entity_id) WHERE (FIND_IN_SET(53, 46, at_category_id.category_id))
  </code></pre>
  
  <p>What I've to do to make this work?</p>