1173. Immediate Food Delivery I

Level: easy; Doordash

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.

Write an SQL query to find the percentage of immediate orders in the table, 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           | 5           | 2019-08-02 | 2019-08-02                  |
| 3           | 1           | 2019-08-11 | 2019-08-11                  |
| 4           | 3           | 2019-08-24 | 2019-08-26                  |
| 5           | 4           | 2019-08-21 | 2019-08-22                  |
| 6           | 2           | 2019-08-11 | 2019-08-13                  |
+-------------+-------------+------------+-----------------------------+
Output:
 
+----------------------+
| immediate_percentage |
+----------------------+
| 33.33                |
+----------------------+
Explanation:
 The orders with delivery id 2 and 3 are immediate while the others are scheduled.

My Solution:

To calculate number of immediate delivery, I use sum and case . For order date equal to dlivery date set this order to 1; otherwise 0. Then the sum of 0 and 1 is the number of immediate delivery.

select round(sum(
case when order_date=customer_pref_delivery_date then 1 else 0 end)*100/count(*),2) 
as immediate_percentage
from Delivery