Find Loyal Customers

Description

Editorial

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3657. Find Loyal Customers

Medium

SQL Schema

Pandas Schema

Table: customer_transactions

+------------------+---------+
| Column Name      | Type    | 
+------------------+---------+
| transaction_id   | int     |
| customer_id      | int     |
| transaction_date | date    |
| amount           | decimal |
| transaction_type | varchar |
+------------------+---------+
transaction_id is the unique identifier for this table.
transaction_type can be either 'purchase' or 'refund'.

Write a solution to find loyal customers. A customer is considered loyal if they meet ALL the following criteria:

Made at least 3 purchase transactions.
Have been active for at least 30 days.
Their refund rate is less than 20% .

Refund rate is the proportion of transactions that are refunds, calculated as the number of refund transactions divided by the total number of transactions (purchases plus refunds).

Return the result table ordered by customer_id in ascending order.

The result format is in the following example.

Example:

Input:

customer_transactions table:

+----------------+-------------+------------------+--------+------------------+
| transaction_id | customer_id | transaction_date | amount | transaction_type |
+----------------+-------------+------------------+--------+------------------+
| 1              | 101         | 2024-01-05       | 150.00 | purchase         |
| 2              | 101         | 2024-01-15       | 200.00 | purchase         |
| 3              | 101         | 2024-02-10       | 180.00 | purchase         |
| 4              | 101         | 2024-02-20       | 250.00 | purchase         |
| 5              | 102         | 2024-01-10       | 100.00 | purchase         |
| 6              | 102         | 2024-01-12       | 120.00 | purchase         |
| 7              | 102         | 2024-01-15       | 80.00  | refund           |
| 8              | 102         | 2024-01-18       | 90.00  | refund           |
| 9              | 102         | 2024-02-15       | 130.00 | purchase         |
| 10             | 103         | 2024-01-01       | 500.00 | purchase         |
| 11             | 103         | 2024-01-02       | 450.00 | purchase         |
| 12             | 103         | 2024-01-03       | 400.00 | purchase         |
| 13             | 104         | 2024-01-01       | 200.00 | purchase         |
| 14             | 104         | 2024-02-01       | 250.00 | purchase         |
| 15             | 104         | 2024-02-15       | 300.00 | purchase         |
| 16             | 104         | 2024-03-01       | 350.00 | purchase         |
| 17             | 104         | 2024-03-10       | 280.00 | purchase         |
| 18             | 104         | 2024-03-15       | 100.00 | refund           |
+----------------+-------------+------------------+--------+------------------+

Output:

+-------------+
| customer_id |
+-------------+
| 101         |
| 104         |
+-------------+

Explanation:

Customer 101:
- Purchase transactions: 4 (IDs: 1, 2, 3, 4)
- Refund transactions: 0
- Refund rate: 0/4 = 0% (less than 20%)
- Active period: Jan 5 to Feb 20 = 46 days (at least 30 days)
- Qualifies as loyal
Customer 102:
- Purchase transactions: 3 (IDs: 5, 6, 9)
- Refund transactions: 2 (IDs: 7, 8)
- Refund rate: 2/5 = 40% (exceeds 20%)
- Not loyal
Customer 103:
- Purchase transactions: 3 (IDs: 10, 11, 12)
- Refund transactions: 0
- Refund rate: 0/3 = 0% (less than 20%)
- Active period: Jan 1 to Jan 3 = 2 days (less than 30 days)
- Not loyal
Customer 104:
- Purchase transactions: 5 (IDs: 13, 14, 15, 16, 17)
- Refund transactions: 1 (ID: 18)
- Refund rate: 1/6 = 16.67% (less than 20%)
- Active period: Jan 1 to Mar 15 = 73 days (at least 30 days)
- Qualifies as loyal

The result table is ordered by customer_id in ascending order.

Code

Testcase

Test Result