WHERE的刺激问题

Question

我在stimulsoft有一个报告，它可以正常使用此查询

SELECT Car.IDCar, Car.NameCar, Car.Code, Car.DriverName, Car.IsTruck,
  CarData.IDCarData, CarData.Start, CarData.End, CarData.Total,
  CarData.Distance, CarData.Weight, CarData.Controller, CarData.Scope,
  CarData.Description, CarData.Date
FROM Car LEFT JOIN
  CarData ON Car.IDCar = CarData.CarID
WHERE CarData.Date= '20150515'

但是当我想像bellow一样使用它时，它不会返回数据

SELECT Car.IDCar, Car.NameCar, Car.Code, Car.DriverName, Car.IsTruck,
  CarData.IDCarData, CarData.Start, CarData.End, CarData.Total,
  CarData.Distance, CarData.Weight, CarData.Controller, CarData.Scope,
  CarData.Description, CarData.Date
FROM Car LEFT JOIN
  CarData ON Car.IDCar = CarData.CarID
WHERE CarData.Date= '20150515' and Car.IsTruck='yes'

我必须提到我的数据是用波斯语写的，所以原始查询是＆gt;

WHERE CarData.Date= '20150515' and Car.IsTruck='بلی'