| 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.
SELECT ROUND(AVG(order_date = customer_pref_delivery_date)*100,2) AS immediate_percentage
FROM Delivery
WHERE (customer_id , order_date ) IN
(
SELECT customer_id , min(order_date) AS order_date
FROM Delivery
GROUP BY customer_id
)
找到 customer_id ,最早的order_date
判斷他是scheduled 還是 immediate
把immediate加起來/全部筆數
學習點 : WHERE (customer_id , order_date ) IN 是指主表的customer_id , order_date 必須跟 SELECT customer_id , min(order_date) AS order_date FROM Delivery GROUP BY customer_id 副表相同
