LeetCode：Database 24.订单最多的客户

Posted 2021-05-21 Xiao Miao

要求：在表 orders 中找到订单数最多客户对应的 customer_number。

数据保证订单数最多的顾客恰好只有一位。
orders表的结构：

| Column            | Type      |
|-------------------|-----------|
| order_number (PK) | int       |
| customer_number   | int       |
| order_date        | date      |
| required_date     | date      |
| shipped_date      | date      |
| status            | char(15)  |
| comment           | char(200) |

orders表：

| order_number | customer_number | order_date | required_date | shipped_date | status | comment |
|--------------|-----------------|------------|---------------|--------------|--------|---------|
| 1            | 1               | 2017-04-09 | 2017-04-13    | 2017-04-12   | Closed |         |
| 2            | 2               | 2017-04-15 | 2017-04-20    | 2017-04-18   | Closed |         |
| 3            | 3               | 2017-04-16 | 2017-04-25    | 2017-04-20   | Closed |         |
| 4            | 3               | 2017-04-18 | 2017-04-28    | 2017-04-25   | Closed |         |

Result Table：

| customer_number |
|-----------------|
| 3               |

分析：
1.要求出订单数最多的customer_number，通过customer_number分组
，将count(customer_number)降序排序，取第一个customer_number即可

SQL语句：

select customer_number
from orders
group by customer_number
order by count(customer_number) desc
limit 1;