Need I change SQL after partition table ?

Hi all,

   I have confuse about partition table in oracle 9i.

  I have a table (my_table) with 100 miliion records and I partitioned this table. But if inside my application, I use select * from my_table --> so, it's better (Assume that I just care about partition, not index, sql, ..) ? Someone said to me, I must change SQL with select * from my_table partition(my_table_par_xxx); (my_table_par_xxx is one of these partitions).

  So if it's right, after I partition table, I must edit SQLs that related with table that partitioned to improve perfomance ? I think that this is a bad idea ! When trace to view execution plan but I can not Oracle query on which partition