Oracle为列表中的每个项目选择一个记录样本

Question

假设我有一个包含id，color，item的表产品。

select distinct color from product

有没有办法不做一堆工会，从产品表中为每种颜色选择最多2条记录？

我希望能够做一些像

这样的事情

select distinct color from product sample 2

Answer 1

不要使用union s！只需使用row_number()：

select p.*
from (select p.*, row_number() over (partition by color order by color) as seqnum
      from product p
     ) p
where seqnum <= 2;

Answer 2

select id, color, item
from   ( select id, color, item, 
                row_number() over (partition by color order by null) as rn
         from   product
       )
where rn <= 2;