Agrupación por dia, mes o año

[Libras]

pues realiza un subquery:

Código SQL:

SELECT CONVERT(fecha,datetime) AS fecha, t1.* FROM(
SELECT CASE @filtro
            WHEN 1 THEN DATEPART(DAY,"Registering Date")
            WHEN 2 THEN DATEPART(MONTH,"Registering Date")
            WHEN 3 THEN DATEPART(YEAR,"Registering Date")
        END AS fecha,
        "Location Code", "Zone Code", "Bin Code", "Item No_", SUM("Quantity"), 
        SUM("Qty_ (Base)")
    FROM dbo.[CRONUS España S_A_$Warehouse Entry]
    WHERE "Registering Date" BETWEEN '2007-01-01' AND '2008-12-31'
    GROUP BY CASE @filtro
            WHEN 1 THEN DATEPART(DAY,"Registering Date")
            WHEN 2 THEN DATEPART(MONTH,"Registering Date")
            WHEN 3 THEN DATEPART(YEAR,"Registering Date")
        END, 
        CASE @filtro 
            WHEN 1 THEN DATEPART(MONTH,"Registering Date")
            WHEN 2 THEN DATEPART(YEAR,"Registering Date") 
        END,
        CASE @filtro 
            WHEN 1 THEN DATEPART(YEAR,"Registering Date") 
        END, "Item No_", "Location Code", "Zone Code", "Bin Code"
) AS t1