1581. Customer Who Visited but Did Not Make Any Transactions

https://leetcode.com/problems/customer-who-visited-but-did-not-make-any-transactions/

Customer Who Visited but Did Not Make Any Transactions - LeetCode

문제 이해하는 데 오래걸렸다.

처음에는 이해를 못해서 discussion 으로 찾아보았고,

그래도 모르겠어서 다음날 다시 도전했더니 이해가 되었다.

select v.customer_id, count(v.customer_id) as count_no_trans
from Visits as v
where visit_id not in (select distinct visit_id from Transactions)
group by customer_id;