586.(Easy)订单最多的客户

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。

表 orders 定义如下：

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

样例输入

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

样例输出

customer_number

3

解释

customer_number 为 '3' 的顾客有两个订单，比顾客 '1' 或者 '2' 都要多，因为他们只有一个订单
所以结果是该顾客的 customer_number ，也就是 3 。
进阶： 如果有多位顾客订单数并列最多，你能找到他们所有的 customer_number 吗？

来源：力扣（LeetCode）

链接：https://leetcode-cn.com/problems/customer-placing-the-largest-number-of-orders

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Solution

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