mysql - 获取 MySQL 中每个组的 top-k

Question

我省略了最后一步之前的步骤。我得到这样的表：year, month, postid, clicks。我如何获得postid每个year, month组的前 k 名？

例如，我有数据：

2012,1,a,5
2012,1,b,3
2012,1,c,8
2012,2,a,2
2012,2,c,5
2012,2,d,6

假设k=2，我想要这样的结果：

2012,1,c,8
2012,1,a,5
2012,2,d,6
2012,2,c,5

Answer 1

试试这个：

select postid, clicks,
    @num := if(@year = @year and @month = month, @num + 1, 1) row_number,
    @year := year year, @month := month month
from (
    select * from t
    order by year, month, clicks desc
) s, (select @num := 0, @year := '', @month := '') init
group by year, month, postid, clicks
having row_number <= 2
order by year, month, clicks desc

在这里提琴