Gruppér efter antal og totalt antal

Du kan bruge en case udtryk baseret på @Month :

SELECT   ProductCode, 
         SUM (CASE WHEN MONTH(EntryDate) = @Month THEN Quantity ELSE 0 END) 
           AS MonthCount,
         SUM (Quantity) AS TotalConount
FROM     ProductMaster
GROUP BY ProductCode

EDIT:
For at besvare det redigerede spørgsmål kan du bruge den samme teknik med count i stedet for sum :

SELECT   ProductCode, 
         COUNT (CASE WHEN MONTH(EntryDate) = @Month THEN Quantity ELSE NULL END) 
           AS MonthCount,
         COUNT (*) AS TotalConount
FROM     ProductMaster
GROUP BY ProductCode