# 1581. Customer Who Visited but Did Not Make Any Transactions
[leetcode](https://leetcode.com/problems/customer-who-visited-but-did-not-make-any-transactions/?envType=study-plan-v2&envId=top-sql-50)
這一題要問　拜訪過的顧客　卻沒有購買的人＋次數
所以我們需要用到left join
因為需要找沒有購買紀錄的 所以購買紀錄必須要是null

WHERE a2.transaction_id IS NULL

然後依照a1.顧客來判斷 誰拜訪後卻沒有購買

# Write your MySQL query statement below
SELECT a1.customer_id ,COUNT(a1.visit_id)  as count_no_trans
FROM Visits a1
LEFT JOIN  Transactions a2
ON a1.visit_id = a2.visit_id
WHERE a2.transaction_id IS NULL
GROUP BY a1.customer_id;