题解 | #第一次购买成功课程的日期，以及购买成功课程的次数#

方法1，在上一题的基础上给子表加字段即可：

with t_user as (
        select o.user_id, count(1) ct
          from order_info o
         where o.date > '2025-10-15'
           and o.status = 'completed'
           and o.product_name in ('C++', 'Java', 'Python')
         group by o.user_id
        having count(1) >= 2
)
select a.user_id, min(a.date) first_buy_date, b.ct cnt 
  from order_info a, t_user b
 where a.user_id = b.user_id
   and a.date > '2025-10-15'
   and a.status = 'completed'
   and a.product_name in ('C++', 'Java', 'Python')
 group by a.user_id
 order by user_id;

方法2，直接通过group by来分组取最小日期和次数，注意having用法：

select a.user_id, min(a.date) first_buy_date, count(1) cnt 
  from order_info a
 where a.date > '2025-10-15'
   and a.status = 'completed'
   and a.product_name in ('C++', 'Java', 'Python')
 group by a.user_id
having count(1) >= 2
 order by user_id;