create table t_1 (primary_id number,  stat_cde varchar2(1))

insert into t_1 values(1, 'R');
insert into t_1 values(1, 'N');
insert into t_1 values(2, 'R');
insert into t_1 values(2, 'E');
insert into t_1 values(3, 'N');
insert into t_1 values(3, 'E');
insert into t_1 values(4, 'N');

commit;

select distinct decode (stat_cde, 'R', 1, 'E', 2, 'N', 3, 99), stat_cde from t_1 order by 1

DECODE(STAT_CDE,'R',1,'E',2,'N',3,99)	STAT_CDE
1	R
2	E
3	N



select primary_id, decode (stat_cde, 'R', 1, 'E', 2, 'N', 3, 99) cde_num, stat_cde,rank()
    over (partition by primary_id
         order by decode (stat_cde, 'R', 1, 'E', 2, 'N', 3, 99)) rnk
  from t_1;

PRIMARY_ID	CDE_NUM	STAT_CDE	RNK
1	1	R	1
1	3	N	2
2	1	R	1
2	2	E	2
3	2	E	1
3	3	N	2
4	3	N	1



SELECT primary_id, stat_cde
  FROM (SELECT primary_id, stat_cde,
               RANK () OVER (PARTITION BY primary_id 
                             ORDER BY DECODE(stat_cde,'R', 1,'E', 2,'N', 3,99)) rnk
          FROM t_1)
 WHERE rnk = 1;

PRIMARY_ID	STAT_CDE
1	R
2	R
3	E
4	N