stimulsoft issues with WHERE

Question

I have a report in stimulsoft, it just work fine with this query

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'

But when I want to use it like bellow, it returns no data

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'

I have to mention that my data are in persian language, so the original query is >

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