Probeer dit
SELECT PerceptionistID, SSNLastFour, SUM(CommissionPay) CommissionPay,
SUM(PTOPay) PTOPay, SUM(HolidayPay) HolidayPay, SUM(Overtime) Overtime, SUM(TotalPay) TotalPay
FROM
(
SELECT PerceptionistID, SSNLastFour, CommissionPay,
PTOPay, HolidayPay, Overtime, TotalPay
FROM [dbo].fnCalculateCommissionForWeekOf(@MondayOfCurrentWeek)
UNION ALL
-- Need to get the following week's data and sum the two together
SELECT PerceptionistID, SSNLastFour, CommissionPay,
PTOPay, HolidayPay, Overtime, TotalPay
FROM [dbo].fnCalculateCommissionForWeekOf(@MondayOfFollowingWeek)
) t
GROUP BY PerceptionistID, SSNLastFour