A function to generate a random URL safe string with PostgreSQL

random_string.sql

create or replace function random_string(nb_bytes integer) 
returns text
as $$
select
    trim('=' 
from
    (
        select
            replace ( (
            select
                replace ( (
                select
                    encode(gen_random_bytes(nb_bytes)::bytea, 'base64')), '/', '_')), '+', '-') 
    )
);
$$ language sql;