​LeetCode刷题实战571：给定数字的频率查询中位数

select
    avg(Number) as median
from
    (select 
        Number,
        SUM(Frequency) OVER(ORDER BY Number) AS DN,
        SUM(Frequency) OVER(ORDER BY Number desc) AS UP,
        SUM(Frequency) OVER() AS TOTAL 
    from
        Numbers) A
where 
    DN >= TOTAL/2  AND  UP >= TOTAL/2

select
    avg(Number) median
from
    (select 
        Number,
        @num as bef,
        @num := @num+Frequency as aft
    from
        (select @num:=0 )B ,Numbers
    order by Number) A
 where
    bef <= @num/2 and aft >= @num/2