如何将SUM(FAMOUNT_BASE)与SUM(FDISCRATE) 的差值，写进下面的语句 ？

select SUM(FAMOUNT_BASE),SUM(FDISCRATE) FROM (

SELECT MA.FCODE,MA.FAMOUNT_BASE,DE.FDISCRATE

FROM BS_MV_SA_MA MA INNER JOIN BS_MV_SA_DE DE

ON MA.FMID=DE.FPID

WHERE TO_CHAR(MA.FBIZTIME,'YYYYMMDD')= TO_CHAR(sysdate,'YYYYMMDD')-1

AND MA.FSTATE=6

AND MA.FORG_STORE_CODE NOT LIKE 'S%'

UNION ALL

SELECT MA.FCODE,MA.FAMOUNT_BASE,DE.FDISCRATE

FROM BS_MV_SA_MA MA

INNER JOIN BS_MV_SA_DE DE

ON MA.FMID=DE.FPID

WHERE TO_CHAR(MA.FBIZTIME,'YYYYMMDD')= TO_CHAR(sysdate,'YYYYMMDD')-1

AND MA.FSTATE=6

AND  MA.FORG_STORE_DE_CODE NOT LIKE 'S%' )