$res=$this->db->from($this->_tableName)->where($where)->select(" buyer_id as buyerId,store_id as storeId,order_amount as orderTotalOnline")->fetchOne();
$res=$this->db->from($this->_tableName)->where($where)->select(" buyer_id as buyerId,store_id as storeId,sum(order_amount) as orderTotalOnline")->fetchOne();