如何使用magento更新查询添加到表列中的现有值？

Trying:

Mage::getModel('module/table')
       ->setId($obj->getId()) //"using _afterSave(Mage_Core_Model_Abstract $obj)"
       ->setCounter(+2) //"want to add to existing integer in table column"
       ->save();
Mage::getModel('module/table')