Guidance needed on an alternative take on common prefix SQL

Hi,

I've seen various Postgres examples here and elsewhere that deal with the old common-prefix problem (i.e. "given 1234 show me the longest match").

I'm in need of a bit of guidance on how best to implement an alternative take. Frankly I don't quite know where to start but I'm guessing it will probably involve CTEs, which is an area I'm very weak on.

So, without further ado, here's the scenario:

Given an SQL filtering query output that includes the following column:
87973891
87973970
87973971
87973972
87973973
87973975
87973976
87973977
87973978
87973979
8797400

The final output should be further filtered down to:
87973891
8797397
8797400

i.e. if $last_digit is present 0–9 inclusive, recursively filter until the remaining string is all the same (i.e. in this case, when $last_digit[0-9] is removed, 8797397 is the same).

So, coming back to the example above:
8797397[0-9] is present
so the "nearest common" I would be looking for is 8797397 because once [0-9] is removed, the 7 is the same on the preceeding digit.

The other two rows ( 87973891 and 8797400) are left untouched because $last_digit is not present in [0-9].

Hope this question makes sense !

Laura