Oracle performance issue Exists

Question

I have a small application for schools and I face the next issue I have a query on Oracle that supposed to fetch all teachers that has a specific student in there classes:

select * from teacher
where exists
 (
   select * from students 
   where teacher.teacher_id = students.teacher_id
     and lower(student_name) like '%john%'
 )

But my query is taking a long time, I tried to use IN or even JOIN but that didn't solve my problem:

select * from teacher
where teacher.teacher_id in
 (
   select students.teacher_id from students 
   where lower(student_name) like '%john%'
 )

and this is using JOIN:

select * from teacher
   JOIN 
      (select students.teacher_id from students 
      where lower(student_name) like '%john%') STUD
ON STUD.teacher_id = teacher_id

actually all are giving me the same result but I found that using EXISTS was the fastest query, but still taking much time -about 10 min-. I think that there might be a way using %rowtype and nested tables to solve the problem... I am a beginner in Oracle, so if some body can help I will be graceful.

Answer 1

select distinct * from teacher 
join student on teacher.teacher_id = student.teacher_id 
where student_name ..

and there should be an index on teacher_id of student