Question

我省略了最后一步之前的步骤。我得到的表格如下：year, month, postid, clicks。如何为每个postid群体获得前缀year, month？

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，我希望结果如下：

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

Answer 1

尝试一下：

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

小提琴here

获取MySQL中每个组的top-k

1 个答案: