1174-ImmediateFoodDeliveryII.sql

-- 1174. Immediate Food Delivery II
-- 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.

-- Create table If Not Exists Delivery (delivery_id int, customer_id int, order_date date, customer_pref_delivery_date date)
-- Truncate table Delivery
-- insert into Delivery (delivery_id, customer_id, order_date, customer_pref_delivery_date) values ('1', '1', '2019-08-01', '2019-08-02')
-- insert into Delivery (delivery_id, customer_id, order_date, customer_pref_delivery_date) values ('2', '2', '2019-08-02', '2019-08-02')
-- insert into Delivery (delivery_id, customer_id, order_date, customer_pref_delivery_date) values ('3', '1', '2019-08-11', '2019-08-12')
-- insert into Delivery (delivery_id, customer_id, order_date, customer_pref_delivery_date) values ('4', '3', '2019-08-24', '2019-08-24')
-- insert into Delivery (delivery_id, customer_id, order_date, customer_pref_delivery_date) values ('5', '3', '2019-08-21', '2019-08-22')
-- insert into Delivery (delivery_id, customer_id, order_date, customer_pref_delivery_date) values ('6', '2', '2019-08-11', '2019-08-13')
-- insert into Delivery (delivery_id, customer_id, order_date, customer_pref_delivery_date) values ('7', '4', '2019-08-09', '2019-08-09')

-- Write your MySQL query statement below
SELECT  
    ROUND(
        AVG(
            order_date = customer_pref_delivery_date -- 即时订单的平均数
        ) * 100, 
        2
    ) AS immediate_percentage
FROM Delivery
WHERE 
    (customer_id, order_date) IN
    (  -- 取用户ID,和首次订单时间
        SELECT 
            customer_id, 
            MIN(order_date) 
        FROM 
            Delivery
        GROUP BY 
            customer_id
    );


-- rank
SELECT 
    ROUND(
        SUM(IF(d.order_date = d.customer_pref_delivery_date, 1, 0)) * 100  
        / 
        COUNT(d.customer_id), 
        2
    ) AS immediate_percentage  
FROM 
(
    select 
        customer_id,  
        order_date,  
        customer_pref_delivery_date,  
        RANK() OVER (PARTITION BY customer_id ORDER BY order_date ASC) AS rk  
    FROM 
        Delivery
) AS d  
WHERE 
    d.rk = 1;

-- best solution
SELECT 
    ROUND(
        100 * SUM(IF(f.order_date = f.customer_pref_delivery_date, 1, 0)) / COUNT(*), 
        2
    ) AS immediate_percentage 
FROM
(
    SELECT 
        * 
    FROM 
    ( 
        SELECT 
            * 
        FROM 
            Delivery AS a 
        ORDER BY 
            a.order_date ASC 
    ) AS b  
    GROUP BY 
        b.customer_id
) AS f