How to query items with identical set of values

Question

I'm looking for an efficient way to query items, that have identical set of values.

I have a following table

C_1  C_2
--------
A    1
A    2
-------
B    1
B    2
B    3
-------
C    1
C    2
-------
D    1
D    2
D    3
-------
E    1
E    2 
-------
F    0
F    2 

I will select the list of items FROM C_1 that have exact the same set of c_2 elements as the given item.

For item A i will have

C
E

For item B i will have

D 

how can it be done in SQL( Oracle 10g )?

---

Here is the create table statement for test purposes

create table t (c_1 varchar2(1), c_2 number);
INSERT into t VALUES('A',    1);
INSERT into t VALUES('A',    2);
INSERT into t VALUES('B',    1);
INSERT into t VALUES('B',    2);
INSERT into t VALUES('B',    3);
INSERT into t VALUES('C',    1);
INSERT into t VALUES('C',    2);
INSERT into t VALUES('D',    1);
INSERT into t VALUES('D',    2);
INSERT into t VALUES('D',    3);
INSERT into t VALUES('E',    1);
INSERT into t VALUES('E',    2); 
INSERT into t VALUES('F',    0);
INSERT into t VALUES('F',    2);

Answer 1

You can use 10g's COLLECT function; since you don't want to see what the c_2 values are you don't even need to cast it.

select c_1
from t
where c_1 != 'A'
group by c_1
having collect(c_2) = (select collect(c_2) from t where c_1 = 'A' group by c_1)
/

Answer 2

create type t_c_2 as table of number;

select one.c_1, two.c_1
from (select t.c_1, CAST(COLLECT(t.c_2) as t_c_2) coll
      from t
      group by t.c_1) one
    ,(select t.c_1, CAST(COLLECT(t.c_2) as t_c_2) coll
      from t
      group by t.c_1) two
where one.coll = two.coll
  and one.c_1 != two.c_1;

I've never used such a construction on a production site, efficiency verification is needed.