R0305.sql

SELECT R.ProductID,
        Varianza = AVG(DATEDIFF(day, ScheduledStartDate, ActualStartDate)),
        Varianza_Ajustada = AVG(NULLIF(DATEDIFF(day, ScheduledStartDate, ActualStartDate), 0))
    FROM Production.WorkOrderRouting R
    GROUP BY R.ProductID
    ORDER BY R.ProductID;