Select Union con Group By

[Libras]

y si haces esto:

Código SQL:

SELECT Tasa, SUM(Importe)
    FROM (
    SELECT DISTINCT [Tasa1] AS Tasa, SUM(Neto1+Neto2) AS Importe FROM Compras
    WHERE (Tasa1 IS NOT NULL)
    GROUP BY Tasa1
    UNION
    SELECT DISTINCT [Tasa2] AS Tasa, SUM(Neto1+Neto2) AS Importe  FROM Compras
    WHERE (Tasa2 IS NOT NULL)
    GROUP BY Tasa2) AS t1
    GROUP BY Tasa
 

saludos!