The number of Rich Customers Problem

Problem

Table: Store

+-------------+------+
| Column Name | Type |
+-------------+------+
| bill_id     | int  |
| customer_id | int  |
| amount      | int  |
+-------------+------+

bill_id is the primary key (column with unique values) for this table. Each row contains information about the amount of one bill and the customer associated with it.

Write a solution to report the number of customers who had at least one bill with an amount strictly greater than 500.

The result format is in the following example.

Examples

Example 1:

Input: Store table:

+---------+-------------+--------+
| bill_id | customer_id | amount |
+---------+-------------+--------+
| 6       | 1           | 549    |
| 8       | 1           | 834    |
| 4       | 2           | 394    |
| 11      | 3           | 657    |
| 13      | 3           | 257    |
+---------+-------------+--------+

Output:

+------------+
| rich_count |
+------------+
| 2          |
+------------+

Explanation: Customer 1 has two bills with amounts strictly greater than 500. Customer 2 does not have any bills with an amount strictly greater than 500. Customer 3 has one bill with an amount strictly greater than 500.

Solution

Method 1 - Distinct Count

Code

SQL

SELECT COUNT(DISTINCT customer_id) AS rich_count FROM Store WHERE amount > 500

Pandas

import pandas as pd

def count_rich_customers(store: pd.DataFrame) -> pd.DataFrame:
    rich_customers = store[store['amount'] > 500]
    num_rich_customers = rich_customers['customer_id'].nunique()
    result_df = pd.DataFrame({'rich_count': [num_rich_customers]})
    return result_df

Problem#

Examples#

Solution#

Method 1 - Distinct Count#

Code#

SQL#

Pandas#