What is the percentage, by number of sales order units, for orders with quantities not greater than 3 and a discount of 0.2?
quantities not greater than 3 refers to OrderQty<3; discount of 0.2 refers to UnitPriceDiscount = 0.2; percentage = DIVIDE(count(SalesOrderID(OrderQty<3 & UnitPriceDiscount = 0.2)), count(SalesOrderID))*100%
SELECT CAST(SUM(CASE WHEN OrderQty < 3 AND UnitPriceDiscount = 0.2 THEN 1 ELSE 0 END) AS REAL) / COUNT(SalesOrderID) FROM SalesOrderDetail