Niko Gamulin Niko Gamulin - 3 months ago 17
SQL Question

How to generate a permutations or combinations of n rows in m columns?

Does anyone know how to create a table with m columns from table of n rows where the values in columns of each row represent a different combination or permutation of values from the original table?

For example the original table has 1 column (number_value) with 3 (n=3) rows:

1
2
3


The table which contains combinations (the order doesn't matter) of two values (m = 2) would be the following:

number1, number2
1,2
1,3
2,3


and the table of permutations would be the following:

number1, number2
1, 2
2, 1
1, 3
3, 1
2, 3
3, 2


The order of rows doesn't matter.

Thank you in advance!

Answer

Combinations:

SELECT T1.x, T2.x
FROM your_table T1
JOIN your_table T2
ON T1.x < T2.x

Permutations:

SELECT T1.x, T2.x
FROM your_table T1
JOIN your_table T2
ON T1.x != T2.x

I am assuming that the values in the original table are unique.

To generalize for larger values of m you need to add more joins.