db2爲給定ID選擇x個隨機行

Question

如果我有兩列 - 一個ID字段和一個可以取10個可能值的分數字段，我怎樣才能爲每個ID選擇5個隨機行？我知道我可以通過從表中選擇以下5個隨機行：每個ID

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

但如何約5行？

Answer 1

可以使用row_number()做到這一點：

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