Convert a row into a column

SELECT
SUBSTR('GREAT',a,1) GREAT
FROM
(
SELECT
ROWNUM a
FROM
DUAL
CONNECT BY
LEVEL <= LENGTH('GREAT')
);

Output :-

G
R
E
A
T

Prepend a Number with 0

Here's an interesting Script :-

DROP TABLE AX;

CREATE TABLE AX ( COL NUMBER );

INSERT INTO AX ( SELECT ROWNUM FROM ALL_OBJECTS WHERE ROWNUM < 10 );

SELECT TO_CHAR(COL,'00') FROM AX;

TO_
---
01
02
03
04
05
06
07
08
09

9 rows selected.