Romanize numbers inside a string (turn "4" to "IV", and so on)

romanize_numbers.sql

create or replace
function romanize_numbers(s text)
returns text
as $$
    select
        string_agg(
            m [1] ||
                case when char_length(m [2]) between 1 and 3
                    then trim(to_char(m [2] :: int, 'RN'))
                else m [2]
                end,
            ''
        )
    from
        regexp_matches(s, '([^0-9]*)([0-9]*)', 'g') m;
$$
language sql
immutable;