Unificar o minimizar consulta MySQL

[huesos52]

Código SQL:

SELECT 
SUM(T1.total1),
SUM(T1.total2),
SUM(T1.total3)
FROM 
(SELECT tabla1.sumando1 AS total1,
              tabla1.sumando2 AS total2,
              tabla1.sumando3 AS total3
 FROM tabla1
UNION ALL
SELECT tabla2.sumando1 AS total1,
              tabla2.sumando2 AS total2,
              tabla2.sumando3 AS total3
 FROM tabla2
UNION ALL
SELECT tabla3.sumando1 AS total1,
              tabla3.sumando2 AS total2,
              tabla3.sumando3 AS total3
 FROM tabla3)T1;