Oracle为列表中的每个项目选择一个记录样本

Question

假设我有一个包含列id，颜色，项目的表格产品。

select distinct color from product 

有没有一种方法没有做一堆的联盟，从产品表中为每种颜色选择最多2条记录？

我很想能够做到像

select distinct color from product sample 2 

Answer 1

不要使用union小号！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;