Formatted question description: https://leetcode.ca/all/1581.html
1581. Customer Who Visited but Did Not Make Any Transactions
Level
Easy
Description
Table: Visits
+-------------+---------+
| Column Name | Type |
+-------------+---------+
| visit_id | int |
| customer_id | int |
+-------------+---------+
visit_id is the primary key for this table.
This table contains information about the customers who visited the mall.
Table: Transactions
+----------------+---------+
| Column Name | Type |
+----------------+---------+
| transaction_id | int |
| visit_id | int |
| amount | int |
+----------------+---------+
transaction_id is the primary key for this table.
This table contains information about the customers who visited the mall.
Write an SQL query to find the IDs of the users who visited without making any transactions and the number of times they made these types of visits.
Return the result table sorted in any order.
The query result format is in the following example:
Visits
+----------+-------------+
| visit_id | customer_id |
+----------+-------------+
| 1 | 23 |
| 2 | 9 |
| 4 | 30 |
| 5 | 54 |
| 6 | 96 |
| 7 | 54 |
| 8 | 54 |
+----------+-------------+
Transactions
+----------------+----------+--------+
| transaction_id | visit_id | amount |
+----------------+----------+--------+
| 2 | 5 | 310 |
| 3 | 5 | 300 |
| 9 | 5 | 200 |
| 12 | 1 | 910 |
| 13 | 2 | 970 |
+----------------+----------+--------+
Result table:
+-------------+----------------+
| customer_id | count_no_trans |
+-------------+----------------+
| 54 | 2 |
| 30 | 1 |
| 96 | 1 |
+-------------+----------------+
Customer with id = 23 visited the mall once and made one transaction during the visit with id = 12.
Customer with id = 9 visited the mall once and made one transaction during the visit with id = 13.
Customer with id = 30 visited the mall once and did not make any transactions.
Customer with id = 54 visited the mall three times. During 2 visits they did not make any transactions, and during one visit they made 3 transactions.
Customer with id = 96 visited the mall once and did not make any transactions.
As we can see, users with IDs 30 and 96 visited the mall one time without making any transactions. Also user 54 visited the mall twice and did not make any transactions.
Solution
For each customer, count the number of visits in table Visits. Join tables Visits and Transactions using visit_id to find the customers who visited but did not make any transactions. Finally, group the result by customer_id.
# Write your MySQL query statement below
select customer_id, count(customer_id) as count_no_trans
from Visits left join Transactions on Visits.visit_id = Transactions.visit_id
where Transactions.visit_id is null
group by customer_id;