SELECT query modification

Question

step-1 select * from t1 --has one column c1 number
step-2 select * from t2 --has two columns c1 number, c2 number (FK of t1.c1), c3 number (FK of t3.c1)
step-3 select * from t3 --has two columns c1 number, c2 varchar2
step-4 SELECT t1.*,t2.*,t3.*,
              ROW_NUMBER() OVER ( ORDER BY t3.c2 ASC
                                        ) RowNumber
          FROM t1
                LEFT JOIN t2 ON t2.c2=t1.c1
                LEFT JOIN t3 ON t3.c1 = t2.c3
step-1
c1
101
102
103
104
105
step-2
c1     c2     c3
1     101     1
2     102     2
3     103     0
step-3
c1     c2
0     c
1     b
2     a
step-4
c1     c1     c2     c3     c1     c2     RowNumber
104     NULL     NULL     NULL     NULL     NULL     1
105     NULL     NULL     NULL     NULL     NULL     2
102     2     102     2     2     a     3
101     1     101     1     1     b     4
103     3     103     0     0     c     5
--In above step-4 you will notice that column c2(near RowNumber column) has NULL value. This is because that the record is present in t1 table but it is missing in detail(t2) table. Here I am trying to sort the records on c2 column of t3 table, which is of varchar type. I want to set the default value of column c2 (near RowNumber column) to 'c' and then perform the sorting.
--the expected output is:
c1     c1     c2     c3     c1     c2     RowNumber
102     2     102     2     2     a     1
101     1     101     1     1     b     2
103     3     103     0     0     c     3
104     NULL     NULL     NULL     NULL     c<--     4
105     NULL     NULL     NULL     NULL     c<--     5
--notice the last two row having '<--'
--how can i achieve this by modifying above step-4 query?

Answer 1

Please find the below given script.
CREATE TABLE T1
  C1 NUMBER NOT NULL
CREATE TABLE T2
  C1 NUMBER NOT NULL,
  C2 NUMBER NOT NULL,
  C3 NUMBER NOT NULL
CREATE TABLE T3
  C1 NUMBER NOT NULL,
  C2 VARCHAR2(20) NOT NULL
INSERT INTO T1 (C1) VALUES ('101');
INSERT INTO T1 (C1) VALUES ('102');
INSERT INTO T1 (C1) VALUES ('103');
INSERT INTO T1 (C1) VALUES ('104');
INSERT INTO T1 (C1) VALUES ('105');
INSERT INTO T2 (C1, C2, C3) VALUES ('1', '101', '1');
INSERT INTO T2 (C1, C2, C3) VALUES ('2', '102', '2');
INSERT INTO T2 (C1, C2, C3) VALUES ('3', '103', '0');
INSERT INTO T3 (C1, C2) VALUES ('0', 'c');
INSERT INTO T3 (C1, C2) VALUES ('1', 'b');
INSERT INTO T3 (C1, C2) VALUES ('2', 'a');--for simplicity i have not created constraints.
Thanks,
Jigs