Question

1565. Unique Orders and Customers Per Month

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Description

Table: Orders

+---------------+---------+
| Column Name   | Type  |
+---------------+---------+
| order_id    | int   |
| order_date  | date  |
| customer_id   | int   |
| invoice     | int   |
+---------------+---------+
order_id is the column with unique values for this table.
This table contains information about the orders made by customer_id.

 

Write a solution to find the number of unique orders and the number of unique customers with invoices > $20 for each different month.

Return the result table sorted in any order.

The result format is in the following example.

 

Example 1:

Input: 
Orders table:
+----------+------------+-------------+------------+
| order_id | order_date | customer_id | invoice  |
+----------+------------+-------------+------------+
| 1    | 2020-09-15 | 1       | 30     |
| 2    | 2020-09-17 | 2       | 90     |
| 3    | 2020-10-06 | 3       | 20     |
| 4    | 2020-10-20 | 3       | 21     |
| 5    | 2020-11-10 | 1       | 10     |
| 6    | 2020-11-21 | 2       | 15     |
| 7    | 2020-12-01 | 4       | 55     |
| 8    | 2020-12-03 | 4       | 77     |
| 9    | 2021-01-07 | 3       | 31     |
| 10     | 2021-01-15 | 2       | 20     |
+----------+------------+-------------+------------+
Output: 
+---------+-------------+----------------+
| month   | order_count | customer_count |
+---------+-------------+----------------+
| 2020-09 | 2       | 2        |
| 2020-10 | 1       | 1        |
| 2020-12 | 2       | 1        |
| 2021-01 | 1       | 1        |
+---------+-------------+----------------+
Explanation: 
In September 2020 we have two orders from 2 different customers with invoices > $20.
In October 2020 we have two orders from 1 customer, and only one of the two orders has invoice > $20.
In November 2020 we have two orders from 2 different customers but invoices < $20, so we don't include that month.
In December 2020 we have two orders from 1 customer both with invoices > $20.
In January 2021 we have two orders from 2 different customers, but only one of them with invoice > $20.

Solutions

Solution 1

# Write your MySQL query statement below
SELECT
  DATE_FORMAT(order_date, '%Y-%m') AS month,
  COUNT(order_id) AS order_count,
  COUNT(DISTINCT customer_id) AS customer_count
FROM Orders
WHERE invoice > 20
GROUP BY month;