;with cte_labor2 as 
(select TimeSheets.*, [HourlyRate] = (select top 1 HourlyRate from WorkerRates 
where WorkerRates.EmployeeID = 
TimeSheets.EmployeeID and TimeSheets.WorkDate >=WorkerRates.RateEffectiveDate and 
TimeSheets.WorkDate >=WorkerRates.RateAddedDate  
ORDER BY WorkerRates.RateEffectiveDate DESC) from TimeSheets)          

select EmployeeID, MONTH(WorkDate) as mWork, YEAR(WorkDate) as YDate, 
SUM(HoursWorked) as HoursWorked, 
SUM(HourlyRate*HoursWorked) as LaborAmount  
from cte_labor2 group by EmployeeID, YEAR(WorkDate), MONTH(WorkDate)