1174_Immediate_Food_Delivery_II.sql

-- Source: https://leetcode.com/problems/immediate-food-delivery-ii/description/?envType=study-plan-v2&envId=top-sql-50

-- 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.

------------------------------------------------------------------------------

-- SQL Schema

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')

-- MS SQL Server Code

WITH cte AS (
    SELECT *,
        ROW_NUMBER() OVER(PARTITION BY customer_id ORDER BY order_date, customer_pref_delivery_date) AS 'rank'
    FROM Delivery
)

SELECT ROUND((100*(SUM(CASE WHEN order_date = customer_pref_delivery_date THEN 1 ELSE 0 END)*1.0)/COUNT(*)),2) AS 'immediate_percentage'
FROM cte
WHERE rank = 1