SQL con sumas de campos

[aposi]

mira si este SQL va mejor

Código SQL [-]
SELECT cob.id_obra,cob.nombre_obra, bf.nom_beneficiario,SUM(pg.importe_pago) AS total_pagos,SUM(dc.importe_desc) AS total_descuentos
FROM obra AS cob
left join  beneficiario AS bf on  cob.id_obra = bf.id_obra
left join  pagos AS pg on bf.id_beneficiario= pg.id_beneficiario
left join  descuentos AS dc on bf.id_beneficiario= dc.id_beneficiario
WHERE 
cob.id_obra= :id_obra