최대 4개 까지 보여준다고 가정하고 했습니다. 

create table t1(c1 integer, c2 char(5))
insert into t1 values (1,'a'),(1,'b'),(1,'c'), (2,'a'),(2,'b'),(2,'c'),(2,'d'), (3,'a'),(3,'b')

select * from t1

C1          C2  
----------- -----
          1 a   
          1 b   
          1 c   
          2 a   
          2 b   
          2 c   
          2 d   
          3 a   
          3 b   

  9 record(s) selected.

select c1,c2,rownumber() over(partition by c1) rn, max(rownumber() over(partition by c1)) over(partition by c1) max from t1

C1          C2    RN                   MAX                
----------- ----- -------------------- --------------------
          1 a                        1                    3
          1 b                        2                    3
          1 c                        3                    3
          2 a                        1                    4
          2 b                        2                    4
          2 c                        3                    4
          2 d                        4                    4
          3 a                        1                    2
          3 b                        2                    2

  9 record(s) selected.

select c1,max(value(case when rn = max-3 then c2 end,''))||

              max(value(case when rn = max-2 then c2 end,''))||

              max(value(case when rn = max-1 then c2 end,''))||

             max(value(case when rn = max-0 then c2 end,''))

from ( select c1,c2,rownumber() over(partition by c1) rn, max(rownumber() over(partition by c1)) over(partition by c1) max from t1 where c1=1 ) a group by c1

C1          2                  
----------- --------------------
          1 a    b    c        

  1 record(s) selected.

rownumber() over() 가 아예 안 먹는데 어떻게 하죠?

DB version이 어떻게 되지요?  os390/400 은 olap function이 안되는것같던데요.

AS400 / DB2 R8 을 씁니다 . AS400이라서 안 먹는건가요?