Formatted question description: https://leetcode.ca/all/1565.html
1565. Unique Orders and Customers Per Month
Level
Easy
Description
Table: Orders
+---------------+---------+
| Column Name | Type |
+---------------+---------+
| order_id | int |
| order_date | date |
| customer_id | int |
| invoice | int |
+---------------+---------+
order_id is the primary key for this table.
This table contains information about the orders made by customer_id.
Write an SQL query to find the number of unique orders and the number of unique users with invoices > $20 for each different month.
Return the result table sorted in any order.
The query result format is in the following example:
Orders
+----------+------------+-------------+------------+
| 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 |
+----------+------------+-------------+------------+
Result table:
+---------+-------------+----------------+
| month | order_count | customer_count |
+---------+-------------+----------------+
| 2020-09 | 2 | 2 |
| 2020-10 | 1 | 1 |
| 2020-12 | 2 | 1 |
| 2021-01 | 1 | 1 |
+---------+-------------+----------------+
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.
Solution
For each month, count the number of distinct orders and the number of distinct customers where invoice > 20. Use date_format to convert the date into the required format. Finally, group the result by the year and the month of order_date.
# Write your MySQL query statement below
select date_format(order_date, '%Y-%m') as month, count(distinct order_id) as order_count, count(distinct customer_id) as customer_count
from Orders
where invoice > 20
group by year(order_date), month(order_date);