Help with a simple SQL

Question

I am having following records
A,B,C,1
A,B,C,2
A,B,C,3
P,Q,R,1
X,Y,Z,1
M,N,O,1
I,J,K,1
I,J,K,9
L,M,N,1
Now my select statement should give me the following result
P,Q,R,1
X,Y,Z,1
M,N,O,1
L,M,N,1
Basically I need those records where the fourth field should have only 1 and shouldn't have any other value. Here all the fields are Key Fields.
Please help me in getting the result.
Nothing is striking me as I am writing SQL after long gap
Thanking you in advance.

Answer 1

Or the same idea as Gabe's, but using analytic function:
SQL> with d as
  2   ( select 'A' c1,'B' c2,'C' c3, 1 c4 from dual union all
  3     select 'A'   ,'B'   ,'C'   , 2    from dual union all
  4     select 'A'   ,'B'   ,'C'   , 3    from dual union all
  5     select 'P'   ,'Q'   ,'R'   , 1    from dual union all
  6     select 'X'   ,'Y'   ,'Z'   , 1    from dual union all
  7     select 'M'   ,'N'   ,'O'   , 1    from dual union all
  8     select 'I'   ,'J'   ,'K'   , 1    from dual union all
  9     select 'I'   ,'J'   ,'K'   , 9    from dual union all
10     select 'L'   ,'M'   ,'N'   , 1    from dual
11   )
12  select c1, c2, c3, c4
13    from (select d.*, count(*) over(partition by c1, c2, c3) cnt from d)
14   where c4 = 1
15     and cnt = 1
16  /
C1 C2 C3         C4
L  M  N           1
M  N  O           1
P  Q  R           1
X  Y  Z           1