query rewrite

Is there any difference between these two:

select CASE WHEN F.f1 IS NULL
            THEN NULL
            ELSE (SELECT X.f2
                    FROM X
                   WHERE code_vl = F.f1)
       END AS f0
from F;

select CASE WHEN F.f1 IS NULL
            THEN NULL
            ELSE ( X.f2)
       END AS f0
  from F , X
 where code_vl(+) = F.f1;

Here are the two plans I get respectively:

SELECT STATEMENT
   TABLE ACCESS - X
   SORT
      TABLE ACCESS - F

30 seconds, 200,000 logical reads

SELECT STATEMENT
   SORT
      HASH JOIN
         TABLE ACCESS - X
         TABLE ACCESS - F

1 second , 12,000 logical reads


?
and if not, why does Oracle not seem to be able to do a hash join in the
first case, but can fine in the second case?

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