1174. Immediate Food Delivery II

Description

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.

Solutions

Solution 1: Subquery

We can use a subquery to first find the first order of each user, and then calculate the proportion of instant orders.

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# Write your MySQL query statement below
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)
        FROM Delivery
        GROUP BY 1
    );

Solution 2: Window Function

We can use the RANK() window function to rank the orders of each user in ascending order by order date, and then filter out the orders with a rank of $1$, which are the first orders of each user. After that, we can calculate the proportion of instant orders.

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# Write your MySQL query statement below
WITH
    T AS (
        SELECT
            *,
            RANK() OVER (
                PARTITION BY customer_id
                ORDER BY order_date
            ) AS rk
        FROM Delivery
    )
SELECT
    ROUND(AVG(order_date = customer_pref_delivery_date) * 100, 2) AS immediate_percentage
FROM T
WHERE rk = 1;