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.
#

# Write your MySQL query statement below

SELECT ROUND(100.0 * SUM(order_date = customer_pref_delivery_date) / COUNT(*), 2) AS immediate_percentage
FROM Delivery
WHERE (customer_id, order_date) IN (
  SELECT customer_id, MIN(order_date)
  FROM Delivery
  GROUP BY customer_id
);