Oracle 18c

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create or replace function randomize (chars varchar2, len int) return varchar2 is 
    val varchar2 (32767);
begin
    for i in 1..len loop
        val := val||substr (chars, round (dbms_random.value (1, length(chars))), 1);
    end loop;

    return val;
end;
/
select randomize (trim (column_value), 10) rnd
from xmlTable ('"123abcdef", "09zyxwvu"')
cross join (select 0 from dual connect by level<=2)


RND


edd13a33cd

yzxyvxzxwv

dddaa13d21

uyxzvu0wvz


with 
function randomize (chars varchar2, len int) return varchar2 is 
    val varchar2 (32767);
begin
    for i in 1..len loop
        val := val||substr (chars, round (dbms_random.value (1, length(chars))), 1);
    end loop;
    return val;
end;
select randomize (trim (column_value), 10) rnd
from xmlTable ('"123abcdef", "09zyxwvu"')
cross join (select 0 from dual connect by level<=2)


RND


db1ac2ebcb

vxyvw9w0wy

a3c2133c3c

v00wzyvxvu