# $571. 给定数字的频率查询中位数
# https://leetcode-cn.com/problems/find-median-given-frequency-of-numbers/

# SQL架构
Create table If Not Exists Numbers (num int, frequency int);
Truncate table Numbers;
insert into Numbers (num, frequency) values ('0', '7');
insert into Numbers (num, frequency) values ('1', '1');
insert into Numbers (num, frequency) values ('2', '3');
insert into Numbers (num, frequency) values ('3', '1');

# Write your MySQL query statement below
select
    avg(num) as median
from
    (
        select
            num,
            frequency,
            sum(frequency) over (
                order by
                    num desc
            ) s1,
            sum(frequency) over (
                order by
                    num asc
            ) s2,
            sum(frequency) over () s3
        from
            Numbers
    ) exp
where
    s1 >= s3 / 2
    and s2 >= s3 / 2;

# clean-up
drop table Numbers;