Generate all possible combinations of strings of certain length in oracle - sql

Question

I have written a program to generate all possible combinations of strings of length two. The program is as follows:
CREATE OR REPLACE PROCEDURE string_combinations
AS
vblString1 VARCHAR2(100);
vblString2 VARCHAR2(100);
vblChr1 NUMBER;
vblChr2 NUMBER;
BEGIN
vblChr1 := 65;
LOOP
SELECT Chr(vblChr1) INTO vblString1 FROM dual;
vblChr2 := 65;
LOOP
vblString2 := vblString1||Chr(vblChr2);
Dbms_Output.put_line(vblString2);
vblChr2:=vblChr2+1;
EXIT WHEN vblChr2=91;
END LOOP;
vblChr1:=vblChr1+1;
EXIT WHEN vblChr1=91;
END LOOP;
END;
/
I have used a loop inside another loop. So, if I have to generate strings of length three, I can simply use another loop. But that would be lengthy if I wish to generate strings of length 5,6,7 or more. How can I use recursion to achieve it?
I am using oracle.

Answer 1

You don't need PL/SQL to generate an alphabetical sequence. You could do it in pure SQL using Row Generator method.
WITH combinations AS
(SELECT chr( ascii('A')+level-1 ) c FROM dual CONNECT BY level <= 26
)
SELECT * FROM combinations
UNION ALL
SELECT c1.c || c2.c FROM combinations c1, combinations c2
UNION ALL
SELECT c1.c
|| c2.c
|| c3.c
FROM combinations c1,
combinations c2,
combinations c3
/
The above would give you all possible combinations c1, c2, c3 for single and two characters. For more combinations, you could just add combinations as c4, c5 etc.

Answer 2

Why not this?
SELECT * FROM a1;
ID NAME
---------- ----------
1 a
2 b
3 c
4 d
5 e
5 rows selected.
SELECT a.id,b.name
FROM (SELECT id FROM a1) a, (SELECT name FROM a1) b
ORDER BY a.id, b.name;
ID NAME
---------- ----------
1 a
1 b
1 c
1 d
1 e
2 a
2 b
2 c
2 d
2 e
3 a
3 b
3 c
3 d
3 e
4 a
4 b
4 c
4 d
4 e
5 a
5 b
5 c
5 d
5 e
25 rows selected.