problem in select query

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here is my rewrite but I think Tamil's did the same thing:

select student_id from (
  select student_id,
   max(decode(course, 'java', student_id)) java,
   max(decode(course, 'c', student_id)) c,
   max(case when course not in ('java', 'c') then 'x' end) x
  from my_table
  group by student_id)
where java is not null and c is not null and x is null