Also Issue in inheriatge class of
in Model/Mysql4/Modulename.php
Mage_Core_Model_Mysql4_Collection_Abstract
to
Mage_Core_Model_Mysql4_Abstract
How to create database module:http://www.amitbera.com/create-an-magento-extension-with-custom-database-table/
Try This
$Collection=Mage::getModel('module/model')->getCollection()->getFieldToFilter('customer_id',$customerId)->addFieldToSelect('*')->setOrder('order_id',DESC);
$collection give array of Record of customer Id
for get one item try this
$Collection->getFirstItem();