ORACLE union order by

select * from (
select a.id,a.oacode,a.custid,a.custname,a.xsz,a.salename,a.communicationtheme,a.communicationproperty,a.communicationtime,a.productmanager,a.creator,a.createdate from technology_flow a 
where a.oastate='正常结束'
union 
select b.id,b.oacode,b.custid,b.custname,b.xsz,b.salename,b.communicationtheme,b.communicationproperty,b.communicationtime,b.productmanager,b.creator,b.createdate  from technology_support b
) t order by t.oacode desc