题解 | #牛客的课程订单分析(七)#

思路：在上一题的基础上，使用coalesce函数，将null值重命名

COALESCE是一个函数， (expression_1, expression_2, ...,expression_n)依次参考各参数表达式，遇到非null值即停止并返回该值。如果所有的表达式都是空值，最终将返回一个空值。

SELECT coalesce(b.name,"GroupBuy") as source ,count(1) from (select *, ROW_NUMBER()over(partition by user_id order by date) as "times", COUNT(1)over(partition by user_id) as "cnt" from order_info where date>"2025-10-15" and status='completed' and product_name in('C++','Java','Python')) a left JOIN client b on a.client_id=b.id where a.cnt>=2 group by b.name order by source