这是因为每一行都调用dbms_random()，因此它可以生成重复的结果.相反，如果您要随机排一行，请尝试如下操作:

That is because dbms_random() is called for each row, so it can generate duplicate results. Instead, if you want one random row, try something like this:

select tid
from (select tid,
             row_number() over (order by dbms_random.value()) as seqnum
      from Train
     ) t
where seqnum = 1;

这将始终返回具有"seqnum = 1"的行，但它将是随机的tid.

This will always return the row with "seqnum = 1", but it will be a random tid.