[SQL문제풀기] Immediate Food Delivery II

Can you solve this real interview question? 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.