LeetCode1581. 进店却未进行过交易的顾客(sql)

题目

思路

分组聚合（计数），过滤掉购物过的

题解

子查询

# Write your MySQL query statement below 
select customer_id, count(customer_id) as count_no_trans from Visits
    where visit_id not in (select visit_id from Transactions)
    group by customer_id;

左连接

# Write your MySQL query statement below 
select customer_id, count(customer_id) 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 customer_id;