derived select can't find table

[wang shuming]

Hi,
  select * , ( select f2
                  from (select f1,f2 from t2 where t2.id=t1.id limit 1 union
all ...  order by f1  ) t2
                  limit 1
                 )  f2
   from t1
 Unknown column ' t1.id' in 'where clause'

Best regard!
Shuming Wang