SQL:
select tt.sid,
       max(tt.anum) as anum,
       max(tt.bnum) as bnum
  from ( 
       select a.aid as sid,
              a.anum,
              null as bnum
         from A
        union 
       select b.bid as sid,
              null as anum,
              b.bnum
         from B
        )tt
 group by tt.sid;


RESULT:

       SID       ANUM       BNUM
---------- ---------- ----------
         1         10         10
         2         10         10
         3         10 
         4                    10