[LeetCode/MySQL50] 1581. Customer Who Visited but Did Not Make Any Transactions

Problem

Solution

# Write your MySQL query statement below
select v.customer_id, count(v.customer_id) as count_no_trans
from Visits v
left outer join Transactions t on v.visit_id = t.visit_id
where t.transaction_id is null
group by v.customer_id;

 

- group by를 통해 customer_id별 aggregation

- left outer join을 활용해 Transaction이 생성되지 않은 id를 살려둘 수 있도록 함

- join 후 transaction_id가 null값인 경우만 추출