LeetCode-in-Java

1174. Immediate Food Delivery II

Medium

SQL Schema

Table: Delivery

+-----------------------------+---------+ 
| Column Name                 | Type    | 
+-----------------------------+---------+ 
| delivery_id                 | int     | 
| customer_id                 | int     | 
| order_date                  | date    | 
| customer_pref_delivery_date | date    | 
+-----------------------------+---------+ 

delivery_id is the primary key 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 an SQL query to find the percentage of immediate orders in the first orders of all customers, rounded to 2 decimal places.

The query 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.

Solution

# Write your MySQL query statement below
SELECT ROUND(AVG(CASE WHEN customer_pref_delivery_date = order_date THEN 1 ELSE 0 END) * 100, 2) AS immediate_percentage
FROM (
    SELECT *,
           DENSE_RANK() OVER(PARTITION BY customer_id ORDER BY order_date ASC) AS dnsrnk
    FROM delivery
) subquery_alias
WHERE subquery_alias.dnsrnk = 1;