Compare all records in a table

Question

Hi,
I have this table
CRN Building Room
1 TH 100
2 TH 100
3 MC 200
4 MC 200
5 MC 100
6 DA 300
7 TH 100
Output:
Table Course
CRN Building Room
1 TH 100
2 TH 100
7 TH 100
3 MC 200
4 MC 200
I want to go through the whole table and and select 2 or more courses that have the same building and room#. I tried
select r.crn, r.building, r.room from course r
where exists (select 1 from course b where b.crn = r.crn and
b.building = r.building and b.room = r.room)
This didn't provide the results desired. Thanks for any help.

Answer 1

Something like this..
SQL> ed
Wrote file afiedt.buf
  1  WITH t as (select 1 as crn, 'TH' as building, 100 as room from dual union all
  2             select 2, 'TH', 100 from dual union all
  3             select 3, 'MC', 200 from dual union all
  4             select 4, 'MC', 200 from dual union all
  5             select 5, 'MC', 100 from dual union all
  6             select 6, 'DA', 300 from dual union all
  7             select 7, 'TH', 100 from dual)
  8  -- end of test data
  9  select *
10  from t
11  where (building,room) in (select building, room
12                            from t
13                            group by building, room
14*                           having count(*) > 1)
SQL> /
       CRN BU       ROOM
         7 TH        100
         2 TH        100
         1 TH        100
         4 MC        200
         3 MC        200
SQL>