oracle how to random select a value out of 2 letters

select chr(121 - 11 * (round(dbms_random.value))) is_successful from dual
or

select case when dbms_random.value(0,1) < 0.5 then 'y' else 'n' end is_successful from dual

or

select translate(dbms_random.string('U',1),'ABCDEFGHIJKLMNOPQRSTUVWXYZ','ynynynynynynynynynynynynyn') from dual

or

select distinct First_Value(is_successful) over(order by dbms_random.value) as is_successfulfrom (select 'n' as is_successful from dual union all select 'y' from dual);

or

substr('yn', dbms_random.value(1,3), 1)