题解 | #每月及截止当月的答题情况#

# mau、新增用户数、 最大新增用户数、 累计用户数
# 新增用户数标记
with table1 as(
    select *,date_format(start_time,'%Y%m') as start_month,
    if(start_time = MIN(start_time)over(partition by uid),1,0) as if_new
    from exam_record
)
select start_month,
count(distinct uid) as mau,
sum(if_new) as month_add_uv,
max(sum(if_new))over(order by start_month) as max_month_add_uv,
sum(sum(if_new))over(order by start_month) as cum_sum_uv
from table1
group by start_month
order by start_month 

# 注意点：执行顺序是先执行group by 然后再执行窗口函数max()over()