SQL | LeetCode 1174. 첫 주문 중 즉시 배송 비율 구하기

Table: Delivery

+-----------------------------+---------+
| Column Name                 | Type    |
+-----------------------------+---------+
| delivery_id                 | int     |
| customer_id                 | int     |
| order_date                  | date    |
| customer_pref_delivery_date | date    |
+-----------------------------+---------+
delivery_id is the column of unique values of this table.
The table holds information about food delivery to customers that make orders at some date and specify a preferred delivery date (on the same order date or after it).

 

If the customer's preferred delivery date is the same as the order date, then the order is called immediate;otherwise, it is called scheduled.

The first order of a customer is the order with the earliest order date that the customer made. It is guaranteed that a customer has precisely one first order.

Write a solution to find the percentage of immediate orders in the first orders of all customers, rounded to 2 decimal places.

The result format is in the following example.

 

Example 1:

Input: 
Delivery table:
+-------------+-------------+------------+-----------------------------+
| delivery_id | customer_id | order_date | customer_pref_delivery_date |
+-------------+-------------+------------+-----------------------------+
| 1           | 1           | 2019-08-01 | 2019-08-02                  |
| 2           | 2           | 2019-08-02 | 2019-08-02                  |
| 3           | 1           | 2019-08-11 | 2019-08-12                  |
| 4           | 3           | 2019-08-24 | 2019-08-24                  |
| 5           | 3           | 2019-08-21 | 2019-08-22                  |
| 6           | 2           | 2019-08-11 | 2019-08-13                  |
| 7           | 4           | 2019-08-09 | 2019-08-09                  |
+-------------+-------------+------------+-----------------------------+
Output: 
+----------------------+
| immediate_percentage |
+----------------------+
| 50.00                |
+----------------------+
Explanation: 
The customer id 1 has a first order with delivery id 1 and it is scheduled.
The customer id 2 has a first order with delivery id 2 and it is immediate.
The customer id 3 has a first order with delivery id 5 and it is scheduled.
The customer id 4 has a first order with delivery id 7 and it is immediate.
Hence, half the customers have immediate first orders.

모든 고객의 첫 주문 중에서 즉시 배송된 비율을 소수점 둘째 자리까지 구하는 질문입니다.

SELECT customer_id, MIN(order_date)
FROM Delivery
GROUP BY customer_id

| customer_id | MIN(order_date) |
| ----------- | --------------- |
| 1           | 2019-08-01      |
| 2           | 2019-08-02      |
| 3           | 2019-08-21      |
| 4           | 2019-08-09      |

각 고객별로 가장 빠른 주문일(= 첫 주문)을 구합니다.

SELECT 
    *
FROM Delivery
WHERE (customer_id, order_date) IN (
    SELECT customer_id, MIN(order_date) 
    FROM Delivery 
    GROUP BY customer_id
);

| delivery_id | customer_id | order_date | customer_pref_delivery_date |
| ----------- | ----------- | ---------- | --------------------------- |
| 1           | 1           | 2019-08-01 | 2019-08-02                  |
| 2           | 2           | 2019-08-02 | 2019-08-02                  |
| 5           | 3           | 2019-08-21 | 2019-08-22                  |
| 7           | 4           | 2019-08-09 | 2019-08-09                  |

첫 주문만 필터링해 가져옵니다.

SELECT 
    round(sum(order_date = customer_pref_delivery_date) / COUNT(*) * 100, 2) AS immediate_percentage
FROM Delivery
WHERE (customer_id, order_date) IN (
    SELECT customer_id, MIN(order_date) 
    FROM Delivery 
    GROUP BY customer_id
);

| immediate_percentage |
| -------------------- |
| 50                   |

첫 주문 중에서 즉시 배송된 비율을 구합니다.