Code:
SELECT DISTINCTROW [Customer Order Query].Order_ID, [Customer Order Query].Date, [Customer Order Query].Customer_ID, [Customer Order Query].Status, Sum([Customer Order Query].Line_total) AS Total, IIf([Total]>50,"yes","no") AS Discount, IIf([Discount]="yes",[Total]*0.9,[Total]) AS [Amount to Pay]
FROM [Customer Order Query]
GROUP BY [Customer Order Query].Order_ID, [Customer Order Query].Date, [Customer Order Query].Customer_ID, [Customer Order Query].Status;
Change Discount and Amount to pay from Group By to Expression.
Dale