MySQL generate all possible combinations from numbers with a certain length - mysql

Question

how to generate all possible combinations from numbers in a MySql table with a certain length? For example 8 numbers.
Only with MySql not together with php.
My table "numbers" contains:
0
1
2
3
4
5
6
7
8
9
I want now to let create all possible combinations in "numbers1".
Like:
00000001
00000002
00000003
00000004

Answer 1

It sounds like you want a cartesian product but I don't get why you want a single column in your output but anyway
select distinct case when u1.id >= u.id then u.id else u1.id end umin,
case when u1.id < u.id then u.id else u1.id end umax
from users u cross join users u1
where u1.id <> u.id
order by umin,umax
The cross join creates the cartesian product the where clause drops those where the combination/permuatation results in the same value eg 1,1 2,2 etc and the distinct dedupes
So given this
MariaDB [sandbox]> select id from users;
+----+
| id |
+----+
| 1 |
| 2 |
| 3 |
| 6 |
| 7 |
| 8 |
| 10 |
| 12 |
| 14 |
| 15 |
| 16 |
| 17 |
| 18 |
| 19 |
| 20 |
+----+
15 rows in set (0.00 sec)
The query results in
+------+------+
| umin | umax |
+------+------+
| 1 | 2 |
| 1 | 3 |
| 1 | 6 |
| 1 | 7 |
| 1 | 8 |
| 1 | 10 |
| 1 | 12 |
| 1 | 14 |
| 1 | 15 |
| 1 | 16 |
| 1 | 17 |
| 1 | 18 |
| 1 | 19 |
| 1 | 20 |
| 2 | 3 |
| 2 | 6 |
| 2 | 7 |
| 2 | 8 |
| 2 | 10 |
| 2 | 12 |
| 2 | 14 |
| 2 | 15 |
| 2 | 16 |
| 2 | 17 |
| 2 | 18 |
| 2 | 19 |
| 2 | 20 |
| 3 | 6 |
| 3 | 7 |
| 3 | 8 |
| 3 | 10 |
| 3 | 12 |
| 3 | 14 |
| 3 | 15 |
| 3 | 16 |
| 3 | 17 |
| 3 | 18 |
| 3 | 19 |
| 3 | 20 |
| 6 | 7 |
| 6 | 8 |
| 6 | 10 |
| 6 | 12 |
| 6 | 14 |
| 6 | 15 |
| 6 | 16 |
| 6 | 17 |
| 6 | 18 |
| 6 | 19 |
| 6 | 20 |
| 7 | 8 |
| 7 | 10 |
| 7 | 12 |
| 7 | 14 |
| 7 | 15 |
| 7 | 16 |
| 7 | 17 |
| 7 | 18 |
| 7 | 19 |
| 7 | 20 |
| 8 | 10 |
| 8 | 12 |
| 8 | 14 |
| 8 | 15 |
| 8 | 16 |
| 8 | 17 |
| 8 | 18 |
| 8 | 19 |
| 8 | 20 |
| 10 | 12 |
| 10 | 14 |
| 10 | 15 |
| 10 | 16 |
| 10 | 17 |
| 10 | 18 |
| 10 | 19 |
| 10 | 20 |
| 12 | 14 |
| 12 | 15 |
| 12 | 16 |
| 12 | 17 |
| 12 | 18 |
| 12 | 19 |
| 12 | 20 |
| 14 | 15 |
| 14 | 16 |
| 14 | 17 |
| 14 | 18 |
| 14 | 19 |
| 14 | 20 |
| 15 | 16 |
| 15 | 17 |
| 15 | 18 |
| 15 | 19 |
| 15 | 20 |
| 16 | 17 |
| 16 | 18 |
| 16 | 19 |
| 16 | 20 |
| 17 | 18 |
| 17 | 19 |
| 17 | 20 |
| 18 | 19 |
| 18 | 20 |
| 19 | 20 |
+------+------+
105 rows in set (0.00 sec)

Answer 2

if the length is fixed it is quite simple, so you could do something like this
DECLARE #number TABLE (num NVARCHAR(1))
INSERT INTO #number
VALUES ('0'),('1'),('2'),('3'),('4'),('5'),('6'),('7'),('8'),('9')
SELECT n1.num + n2.num + n3.num + n4.num
FROM #number n1, #number n2, #number n3, #number n4
if the number is variable you could either build the sql-command and execute it using sp_execute #cmd or you can create a table-value-function for it.
Edit: I just overread the "mysql"-part. the solution above is coded in TSQL (using MS SqlServer). I am not completely sure, but the only thing you have to change should be the declaration of the variable.
CREATE TEMPORARY TABLE #number (num NVARCHAR(1))
And if I am not mistaken instead of using sp_executeto execute a command you can use something like
PREPARE cmd FROM 'SELECT ...'
EXECUTE cmd