2024-01-25 力扣高频SQL50题目1174. 即时食物配送

题目如下：

配送表: Delivery

+-----------------------------+---------+
| Column Name                 | Type    |
+-----------------------------+---------+
| delivery_id                 | int     |
| customer_id                 | int     |
| order_date                  | date    |
| customer_pref_delivery_date | date    |
+-----------------------------+---------+
delivery_id 是该表中具有唯一值的列。
该表保存着顾客的食物配送信息，顾客在某个日期下了订单，并指定了一个期望的配送日期（和下单日期相同或者在那之后）。

如果顾客期望的配送日期和下单日期相同，则该订单称为「即时订单」，否则称为「计划订单」。

「首次订单」是顾客最早创建的订单。我们保证一个顾客只会有一个「首次订单」。

编写解决方案以获取即时订单在所有用户的首次订单中的比例。保留两位小数。

------

这个题目还是很有意思的。

一开始，我以为即时订单总量/所有用户首次订单数总量。

-- 不对

-- select round((sum(if(order_date=customer_pref_delivery_date,1,0))/count(distinct customer_id )),4)*100 as immediate_percentage from Delivery

-- 不对

-- select round((sum(if(order_date=customer_pref_delivery_date,1,0))/(select distinct count( customer_id )from Delivery ))*100,2) as immediate_percentage from Delivery

-- 不对

-- select round((sum(if(order_date=customer_pref_delivery_date,1,0))/(select COUNT(DISTINCT customer_id) from Delivery ))*100,2) as immediate_percentage from Delivery

-- 我看了下其他人答案，发现自己理解错了。

"即时订单在所有用户的首次订单中的比例"。

应该是所有用户的首次订单中的即时订单总数 / 所有用户的首次订单量。

所以，需要框定范围，首次订单。

-- 不对

-- select round((sum(if(order_date=customer_pref_delivery_date,1,0))/(select COUNT(DISTINCT customer_id) from Delivery ))*100,2) as immediate_percentage from Delivery group by customer_id

正确的写法：

-- 没用rownumber的解法

-- select round((sum(if(order_date=customer_pref_delivery_date,1,0))/(select COUNT(DISTINCT customer_id) from Delivery ))*100,2) as immediate_percentage from Delivery where (customer_id, order_date) in (

select customer_id, min(order_date)

from delivery

group by customer_id )

-- 用rownumber的解法

-- SELECT round((sum(if(order_date=customer_pref_delivery_date,1,0))/(SELECT COUNT(DISTINCT customer_id) FROM Delivery))*100, 2) AS immediate_percentage

-- FROM

(SELECT *, ROW_NUMBER() OVER(PARTITION BY customer_id ORDER BY order_date) AS rn FROM Delivery) AS subquery WHERE rn = 1;