select 表C.Value from 表A,表B,表C where 表A.number=表B.number and 表B.number=表C.number and 表A.level = 2 and 表A.time=to_date('20120311','yyyy/mm/dd') and 表C.time=to_date('20120311','yyyy/mm/dd')

select C.Value 
from A,B,C 
where A.number=B.number and 
      A.number=C.number and 
      A.level = 2 and 
      A.time=C.time and            
      A.time=to_date('20120311','yyyy/mm/dd')

------解决方案--------------------
SQL code

select C.Value 
from A,B,C 
where A.number=B.number and 
      A.number=C.number and 
      A.level = 2 and 
      A.time=C.time and            
      to_char(A.time,'yyyy/mm/dd')='20120311'