别人原一个问帖,我用这个方法解决,觉得有点笨啦,哈哈

with tt as (select 1 B from dual
            UNION ALL
            select 4 b from dual
            UNION ALL
            select 8 b from dual
            UNION ALL
            select 9 b from dual
            UNION ALL
            select 12  from dual)
select b
from (select b,row_number() over(order by dbms_random.value) rn from tt) 
where rn=1