１．在后台中新建产品属性salestotal用作销量排序
２．新建Tang/ProductSales模块
３．配置模块的config.xml文件

<?xml version="1.0"?>
<config>

    <modules>
        <Tang_ProductSales>
            <version>0.1.0</version>
       </Tang_ProductSales>
    </modules>

    <frontend>

        <routers>
            <productsales>
                <use>standard</use>
                <args>
                    <module>Tang_ProductSales</module>
                    <frontName>productsales</frontName>
                </args>
            </productsales>
        </routers>

        <layout>
            <updates>
                <productsales>
                    <file>productsales.xml</file>
                </productsales>
            </updates>
        </layout>

    </frontend>

    <global>

        <models>
            <productsales>
                <class>Tang_ProductSales_Model</class>
                <resourceModel>productsales_resource</resourceModel>
            </productsales>
            <!-- st 数据库资源模型配置 -->
            <productsales_resource>
                <class>Tang_ProductSales_Model_Resource</class>
                <deprecatedNode>productsales_mysql4</deprecatedNode>
                <entities>
                    <catalog_product_entity_varchar>
                        <table>catalog_product_entity_varchar</table>
                    </catalog_product_entity_varchar>
                </entities>
            </productsales_resource>
            <!-- end 数据库资源模型配置 -->
        </models>

        <events>
            <checkout_onepage_controller_success_action>
                <observers>
                    <productsales>
                        <!--
                        此处可以model、object、singleton
                        1. model和object是等效的且它们都将使用Mage::getModel(...)方法来进行初始化
                        2. 而singleton将使用Mage::getSingleton(...)来初始化
                        -->
                        <type>model</type>
                        <class>productsales/observer</class>
                        <method>preOrderSubmitInsertProductSales</method>
                    </productsales>
                </observers>
            </checkout_onepage_controller_success_action>
        </events>

        <helpers>
            <productsales>
                <class>Tang_ProductSales_Helper</class>
            </productsales>
        </helpers>

        <blocks>
            <productsales>
                <class>Tang_ProductSales_Block</class>
            </productsales>
        </blocks>

        <resources>
            <productsales_write>
                <connection>
                    <use>core_write</use>
                </connection>
            </productsales_write>
            <productsales_read>
                <connection>
                    <use>core_read</use>
                </connection>
            </productsales_read>
        </resources>

    </global>
</config>

４．配置监听时间，当提交订单后，订单中的产品销量属性加一

<?php
class Tang_ProductSales_Model_Observer extends  Mage_Catalog_Model_Observer
{
    public function preOrderSubmitInsertProductSales(Varien_Event_Observer $observer){
        $order = new Mage_Sales_Model_Order();
        $incrementId = Mage::getSingleton('checkout/session')->getLastRealOrderId(); //订单ID
        $order = Mage::getModel('sales/order')->loadByIncrementId($incrementId); //订单信息
        $orderItems = $order->getItemsCollection();

        foreach ($orderItems as $item) {
            //获取指定产品对象
            $prcProject = Mage::getModel('catalog/product')->load($item->getProductId());
            $attrProject = Mage::getModel('eav/entity_attribute')->load('renqi','attribute_code'); //获取指定属性标识码的属性信息
            $entypeid = $attrProject->getEntity_type_id(); //Eav类型
            $attrid = $attrProject->getAttribute_id(); //属性ID
            $storeid = 0; //商店ID
            $entityid = $item->getProductId(); //产品ID
            $_product = Mage::getResourceModel('reports/product_collection')
                ->addOrderedQty()
                ->addAttributeToFilter('sku', $prcProject->getSku())
                ->setOrder('ordered_qty', 'desc')
                ->getFirstItem();
            $svalue = (int)$_product->getOrderedQty();
//            $svalue = (int)$_product->addOrderedQty() + $prcProject->getSalestotal(); //销量累加
            if($svalue >0){
                $ifused = true;
            }else{
                $ifused = false;
            }
            Mage::getResourceSingleton('productsales/salestotal')->updProductSalesTotal($entypeid, $attrid, $storeid, $entityid, $svalue, $ifused);

        }
        return $this;
    }
}

４．对销量属性进行写入：

<?php
class Tang_ProductSales_Model_Resource_Salestotal extends Mage_Core_Model_Resource_Db_Abstract
{
    protected function _construct() {
        $this->_init("productsales/catalog_product_entity_varchar","value_id");
    }

    /**
     * 添加产品销量到产品信息中
     * @param int $entypeid eav类型
     * @param int $attrid 属性ID
     * @param int $storeid 商店ID
     * @param int $entityid 产品ID
     * @param varchar $svalue 销量
     * @param bool $ifused 是否已存在
     * @return number
     */

    public function updProductSalesTotal($entypeid, $attrid, $storeid, $entityid, $svalue, $ifused){
        $selfread = $this->_getConnection('productsales_write');
        $table = $this->getTable('productsales/catalog_product_entity_varchar');
        //存入数组的数据
        $sdata = array("entity_type_id"=>$entypeid, 'attribute_id'=>$attrid, 'store_id'=>$storeid, 'entity_id'=>$entityid, 'value'=>$svalue);
        //查询条件
        if($ifused){
            $swhere = " attribute_id=$attrid"." AND entity_id=$entityid";
            //执行更新操作
            return $selfread->update($table, $sdata, $swhere);
        }else{
            //执行插入操作
            return $selfread->insert($table, $sdata);
        }
    }
}

具体可以参考旺铺商城的项目