Problem: 1581. 进店却未进行过交易的顾客

思路

👨‍🏫 山山山林老木

• 左连接查询
• 筛选 transation_id 为 null 的值
• group by customer_id

Code

select v.customer_id ,count(customer_id) count_no_trans
from Visits v 
left join Transactions t 
on v.visit_id = t.visit_id
where transaction_id is null
group by customer_id;