How to fill same value with child row - oracle

Question

In Oracle, i want to fill child to lowest parent value.
that is query and result
query :
SELECT col1,col2 FROM DATA
result :
+-----------+------+
| col1 | col2 |
+-----------+------+
| 001 | a |
| 001001 | b |
| 001002 | c |
| 001003 | d |
| 001003001 | e |
| 001003002 | f |
| 002 | g |
| 003 | h |
| 003001 | i |
| 003002 | j |
+-----------+------+
col1 is key. and child index have parent index.
i want to make this result
+------+------+------+------+
| col1 | col2 | col3 | col4 |
+------+------+------+------+
| a | b | b | b |
| a | c | c | c |
| a | d | e | e |
| a | d | f | f |
| g | g | g | g |
| h | i | i | i |
| h | j | j | j |
+------+------+------+------+
if parent have no child, child columns fill to parent.
how can i make this result?...
thank you.

Answer 1

One way to do this:
select c1, coalesce(c2, c1) c2, coalesce(c3, c2, c1) c3, coalesce(c4, c3, c2, c1) c4
from (select substr(path, 2, 1) c1, substr(path, 4, 1) c2,
substr(path, 6, 1) c3, substr(path, 8, 1) c4
from (select sys_connect_by_path(col2, ' ') path
from data
where connect_by_isleaf = 1
connect by substr(col1, 1, length(prior col1)) = prior col1
and length(prior col1) + 3 = length(col1)
start with length(col1) = 3 ) )
Assuming that values in col2 are 1-char long You can do it like above. Otherwise you have to change substr(path, ..., ...) using instr() or regular expressions.
The inner query is hierarchical where I'm selecting only whole path from leaf rows. Outer queries puts data into particular columns dealing with null values.
If You work on Oracle 11g or above You can probably achieve this in more elegant way using Recursive Subquery Factoring.
Test data and output:
create table data (col1 varchar2(10), col2 varchar2(1));
insert into data values ('001', 'a');
insert into data values ('001001', 'b');
insert into data values ('001002', 'c');
insert into data values ('001003', 'd');
insert into data values ('001003001', 'e');
insert into data values ('001003002', 'f');
insert into data values ('002', 'g');
insert into data values ('003', 'h');
insert into data values ('003001', 'i');
insert into data values ('003002', 'j');
C1 C2 C3 C4
-- -- -- --
a b b b
a c c c
a d e e
a d f f
g g g g
h i i i
h j j j
7 rows selected