怎么将两个DataTimepicker控件的中间日期传给worktime？

   sql = string.Format(@" select * from {0} where worktime >='{1}' and worktime <'{2}'", TableName, starttime.ToString("yyyy-MM-dd"), endtime.AddDays(1).ToString("yyyy-MM-dd")); 

                DoctorDutyDto = dalQuery.Query(dtpTimeBegin.Value.Date, dtpTimeEnd.Value.Date)