using case when with count and partition by functions in an oracle query

without the rest of the query and without example data, expected result and real result  ?
a guess :  the count(*) counts over student , so wil count 2 when the students attents 2 times

to get 1  change every sum value other then 0 to 1  
example
select U.TABLE_NAME, COLUMN_NAME
,CASE CASE WHEN column_name like 'C%' THEN count(*) over (partition by column_name) ELSE 0 end
 WHEN 0 THEN 0
 ELSE 1
 END "CNT1"
,CASE WHEN column_name like 'C%' THEN count(*) over (partition by column_name) ELSE 0 end "CNT2"
from user_tab_columns U

agree with flow01;
unless we know more about your data and the expected result we have to guess too much.

e.g.
a correlated subquery might be a reasonable solution here but I have no way of knowing if that is true

select
  s.studentid
,  (select 1 from Attendance_Code ac
        where s.studentid = ac.studentid and ac.Att_Code in ('HB') AND s.grade_level = '12' ) "12"
, ...
from STUDENTS s
...

perhaps a more traditional approach would suit you better?

SELECT
      s.studentid
    , s.grade_level
    , ac.hb
FROM students s
INNER JOIN (
      SELECT
            studentid
          , MAX(CASE WHEN Att_Code IN ('HB') THEN 1 ELSE 0 END) AS hb
      FROM Attendance_Code
      GROUP BY
            studentid
    ) ac ON s.studentid = ac.studentid

Select allOpen in new window

Just like your previous question:
We aren't understanding your requirements.  Please create a simple test case that will show us what you are trying to
accomplish.

>> but it doesn't seem to work as expected

OK, what does it return that it shouldn't?  
What doesn't it return that it should?
Does it cause the server to reboot?

What does it do or not do based on your expectations?

For 11 and 12:

select count(case when "11" > 0 then 1 end) total_for_11,
	count(case when "12" > 0 then 1 end) total_for_12
from (
	select student_number,
		count(case when att_code='HB' and grade_level='11' then 1 end) "11",
		count(case when att_code='HB' and grade_level='12' then 1 end) "12"
	from tab1
	group by student_number
)
/

Select allOpen in new window

slightvw

The following worked great!  Thanks so much!!!
select count(case when "12" > 0 then 1 end) total_for_12
from (
      select student_number, count(case when att_code='HB' and grade_level='12' then 1 end) "12"
      from tab1
      group by student_number
)