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

😎풀이

1. Visits와 Transactions LEFT JOIN
2. 방문하지 않은 고객은 검색 조건에서 제외
3. customer_id를 기준으로 그룹화
4. 미거래 방문 수에 따라 오름차 순 정렬렬

SELECT 
    v.customer_id,
    COUNT(*) AS count_no_trans
FROM
    Visits AS v
LEFT JOIN
    Transactions AS t
ON
    v.visit_id = t.visit_id
WHERE
    t.visit_id IS NULL
GROUP BY
    v.customer_id
ORDER BY
    count_no_trans;