题解 | #牛客的课程订单分析(五)#

select a.user_id,a.first_buy_date,c.second_buy_date,a.cnt from
(select distinct user_id,min(date) as first_buy_date,count(*)as cnt
from order_info
where product_name in ('C++','Python','Java')
and status='completed'
and date>'2025-10-15'
group by user_id having count(*)>=2) as a,

(select user_id,date as second_buy_date from
(select user_id, date, dense_rank()over(partition by user_id order by date) as posn
from order_info
where product_name in ('C++','Python','Java')
and status='completed'
and date>'2025-10-15'
)b
where b.posn=2) c
where a.user_id=c.user_id
order by a.user_id