sql基本运算

SELECT  (PX/(AGFX+PG+ZF+QYZ+KZZ)) as MJB FROM(
select 
case 
when PX is null then 0 else PX 
end as PX, 
case 
when AGFX is null then 0 else AGFX 
end as AGFX, 
case 
when PG is null then 0 else PG 
end as PG, 
case 
when ZF is null then 0 else ZF 
end as ZF, 
case 
when QYZ is null then 0 else QYZ 
end as QYZ, 
case 
when KZZ is null then 0 else KZZ 
end as KZZ
from gp_qjt_mjfh Where GPDM = '002456') A