Magento Search Results – Sort by Ordered Quantity

One way of solving your issue is; by adding additional sort option like Relevance/Position sort option. In order for you to add a "ordered quantity" option you need to do the following:

• First copy Config.php from app/code/core/Mage/Catalog/Model/Config.php to app/code/local/Mage/Catalog/Model/Config.php and replace this function getAttributeUsedForSortByArray() with the following code:

public function getAttributeUsedForSortByArray()
{
    $options = array(
        'position'  => Mage::helper('catalog')->__('Position'),
        'ordered_qty'  => Mage::helper('catalog')->__('Ordered Qty'),
    );
    foreach ($this->getAttributesUsedForSortBy() as $attribute) {
        /* @var $attribute Mage_Eav_Model_Entity_Attribute_Abstract */
        $options[$attribute->getAttributeCode()] = $attribute->getStoreLabel();
    }

    return $options;
}

• Second copy Toolbar.php from app/code/core/Mage/Catalog/Block/Product/List/Toolbar.php to app/code/local/Mage/Catalog/Block/Product/List/Toolbar.php and replace this function setCollection() with the following code:

public function setCollection($collection)
{
    $this->_collection = $collection;

    $this->_collection->setCurPage($this->getCurrentPage());

    // we need to set pagination only if passed value integer and more that 0
    $limit = (int)$this->getLimit();
    if ($limit) {
        $this->_collection->setPageSize($limit);
    }
    if ($this->getCurrentOrder()) {
        if($this->getCurrentOrder() == 'ordered_qty') {
            $this->getCollection()->getSelect()
                 ->joinLeft('sales_flat_order_item AS so', 'e.entity_id = so.product_id', 'SUM(so.qty_ordered) AS ordered_qty')
                 ->group('e.entity_id')->order('ordered_qty ' . $this->getCurrentDirection());
        } else {
            $this->_collection->setOrder($this->getCurrentOrder(), $this->getCurrentDirection());
        }
    }
    return $this;
}

• Third to set "Ordered Qty" sort option as default for Search Result and Advance Search Result add/edit local.xml under your active theme folder app/design/frontend/your_package/your_theme/layout/local.xml and add the following:

<?xml version="1.0" encoding="UTF-8"?>
<layout>
    <catalogsearch_result_index>
        <reference name="search_result_list">
            <action method="setDefaultDirection"><param>desc</param></action>
            <action method="setSortBy"><param>ordered_qty</param></action>
        </reference>
    </catalogsearch_result_index>
    <catalogsearch_advanced_result>
        <reference name="search_result_list">
            <action method="setDefaultDirection"><param>desc</param></action>
            <action method="setSortBy"><param>ordered_qty</param></action>
        </reference>
    </catalogsearch_advanced_result>
</layout>

I hope this will help you.