如何构建DQL查询

Question

我的查询

SELECT * FROM Reservations_Interval LEFT JOIN Reservations_Booking 
ON 
Reservations_Interval.id = Reservations_Booking.interval_id
WHERE 
service_id = 8

---

return Doctrine_Query::create()  
                ->select('RI.*, RB.*')
                ->from('Reservations_Interval  r')
                ->leftJoin('r.Reservations_Booking rp')
                ->where('date >= ? AND date <= ? AND service_id = ? ',  array('2013-05-27', '2013-05-29',9))
                ->execute(); 

我收到错误

错误：

Unknown relation alias Reservations_Booking

出了什么问题？