Compare occurence of chars in PostgreSQL string

I have some data like this: | metaphone | lag | | -------- | -------------- | | FLKSW| [null]| | PPS| FLKSW| | PPS| PPS| | PSP| PPS| And I want to compare the string values in both columns on the folowing condition: they're similar (assign some value, like 1) if they share at least 2 chars. Otherwise, they're not similar. So in the example, PPS and PSP would be similar. How can this substring comparison be achieved? I know one approach would be to extract substrings and manually compare them, but it feels hacky and I don't know the maximum number of chars that can occur.