Oracle SQL use previous column value to lookup next row - sql

Question

What I currently have:
ID FROM_REF TO_REF
--- -------- ----
1 1 10
1 2 3
1 3 4
1 3 5
1 5 6
1 6 7
1 7 9
1 8 11
1 9 8
1 10 2
What's needed is the SORT column which I can use to sort according later on:
ID FROM_REF TO_REF SORT
--- -------- ---- ----
1 1 10 1
1 10 2 2
1 2 3 3
1 3 4 4
1 4 5 5
1 5 6 6
1 6 7 7
1 7 9 8
1 9 8 9
1 8 11 10
NOTE: TO_REF column indicate next FROM_REF.
How do I write SQL to achieve the SORT column as result?
Please help.

Answer 1

You can use a RECURSIVE function.
WITH X (ID, FROM_REF, TO_REF) AS
(
SELECT ID, FROM_REF, TO_REF
FROM tbl
WHERE FROM_REF = 1
UNION ALL
SELECT tbl.ID, tbl.FROM_REF, tbl.TO_REF
FROM tbl
JOIN X
ON tbl.ID = X.ID
AND tbl.FROM_REF = X.TO_REF
)
SELECT ID, FROM_REF, TO_REF
FROM X
ID | FROM_REF | TO_REF
-: | -------: | -----:
1 | 1 | 10
1 | 10 | 2
1 | 2 | 3
1 | 3 | 4
1 | 4 | 5
1 | 5 | 6
1 | 6 | 7
1 | 7 | 9
1 | 9 | 8
1 | 8 | 11
dbfiddle here

Answer 2

A simple hierarchical query, I presume.
SQL> with test (from_ref, to_ref) as
2 (select 1, 10 from dual union
3 select 2, 3 from dual union
4 select 3, 4 from dual union
5 select 4, 5 from dual union
6 select 5, 6 from dual union
7 select 6, 7 from dual union
8 select 7, 9 from dual union
9 select 8, 11 from dual union
10 select 9, 8 from dual union
11 select 10, 2 from dual
12 )
13 select from_ref, to_ref, level rn
14 from test
15 connect by from_ref = prior to_ref
16 start with from_ref = (select min(from_ref) from test);
FROM_REF TO_REF RN
---------- ---------- ----------
1 10 1
10 2 2
2 3 3
3 4 4
4 5 5
5 6 6
6 7 7
7 9 8
9 8 9
8 11 10
10 rows selected.
SQL>