By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
| S | N | SUBSTRING |
|---|---|---|
| aaa,asdf,2,3,3,4,5,,123,,,zz | 1 | aaa |
| aaa,asdf,2,3,3,4,5,,123,,,zz | 2 | asdf |
| aaa,asdf,2,3,3,4,5,,123,,,zz | 3 | 2 |
| aaa,asdf,2,3,3,4,5,,123,,,zz | 4 | 3 |
| aaa,asdf,2,3,3,4,5,,123,,,zz | 5 | 3 |
| aaa,asdf,2,3,3,4,5,,123,,,zz | 6 | 4 |
| aaa,asdf,2,3,3,4,5,,123,,,zz | 7 | 5 |
| aaa,asdf,2,3,3,4,5,,123,,,zz | 8 | null |
| aaa,asdf,2,3,3,4,5,,123,,,zz | 9 | 123 |
| aaa,asdf,2,3,3,4,5,,123,,,zz | 10 | null |
| aaa,asdf,2,3,3,4,5,,123,,,zz | 11 | null |
| aaa,asdf,2,3,3,4,5,,123,,,zz | 12 | zz |