@@ -1,3 +1,85 @@
+-- Problem:
+
+/*
+Table: Visits
+
++-------------+---------+
+| Column Name | Type |
++-------------+---------+
+| visit_id | int |
+| customer_id | int |
++-------------+---------+
+visit_id is the column with unique values 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 column with unique values for this table.
+This table contains information about the transactions made during the visit_id.
+
+
+Write a solution 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 result format is in the following example.
+
+
+
+Example 1:
+
+Input:
+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 |
++----------------+----------+--------+
+Output:
++-------------+----------------+
+| customer_id | count_no_trans |
++-------------+----------------+
+| 54 | 2 |
+| 30 | 1 |
+| 96 | 1 |
++-------------+----------------+
+Explanation:
+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:
+
 SELECT DISTINCT Visits.customer_id, COUNT(Visits.visit_id) AS count_no_trans FROM Visits
 LEFT JOIN Transactions ON Visits.visit_id = Transactions.visit_id
 WHERE transaction_id IS NULL