题目
配送表: Delivery
+-----------------------------+---------+
| Column Name | Type |
+-----------------------------+---------+
| delivery_id | int |
| customer_id | int |
| order_date | date |
| customer_pref_delivery_date | date |
+-----------------------------+---------+
delivery_id 是表的主键。
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」。
写一条 SQL 查询语句获取即时订单所占的比例， 保留两位小数。
查询结果如下所示：
Delivery 表:
+-------------+-------------+------------+-----------------------------+
| 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 |
+-------------+-------------+------------+-----------------------------+
Result 表:
+----------------------+
| immediate_percentage |
+----------------------+
| 33.33 |
+----------------------+
2 和 3 号订单为即时订单，其他的为计划订单。
解答
order_date 与 customer_pref_delivery_date 相同即为即时订单
计算即时订单的数量
select count(D1.delivery_id)
from Delivery as D1
where D1.order_date = D1.customer_pref_delivery_date
计算总订单的数量
select count(D2.delivery_id)
from Delivery as D2
两者相除保留小数即可
select round((select count(D1.delivery_id)
from Delivery as D1
where D1.order_date = D1.customer_pref_delivery_date) /
(select count(D2.delivery_id)
from Delivery as D2), 4
) * 100
as immediate_percentage
别的解答
条件选择
select round(
sum(case when order_date=customer_pref_delivery_date then 1 else 0 end) /
count(*)
,4)*100
as immediate_percentage
from Delivery
select round(
sum(if(order_date=customer_pref_delivery_date, 1, 0)) /
count(*)
,4)*100
as immediate_percentage
from Delivery
逻辑真值
select round(
sum(order_date=customer_pref_delivery_date) /
count(*)
,4)*100
as immediate_percentage
from Delivery
