db2 为给定的 id 选择 x 个随机行

Question

如果我有两列 - 一个 ID 字段和一个可以取 10 个可能值的分数字段，我如何为每个 ID 选择 5 个随机行？我知道我可以使用以下方法从表中随机选择 5 行：

select *, rand() as idx
from mytable 
order by idx fetch first 5 rows only

但是每个 ID 5 行怎么样？

Answer 1

您可以使用row_number()：

select t.*
from (select t.*,
             row_number() over (partition by idx order by rand()) as seqnum
      from mytable t
     ) t
where seqnum <= 5;