题解 | #牛客的课程订单分析(五)#

难点在于第二次购买时间，利用窗口函数解决

select u.user_id, max(if(u.date_rk = 1, u.date ,null)), max(if(u.date_rk = 2, u.date ,null)), max(u.cnt)
from
(select user_id,date, 
dense_rank() over(partition by user_id order by date) as date_rk,
count(user_id) over(partition by user_id) as cnt
from order_info 
where date > '2025-10-15' 
and product_name in ('C++','Python','Java')
and status = 'completed') as u
where u.cnt > 1
group by user_id
order by user_id;