难度系数： 简单
表: Orders
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| Column Name | Type |
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| order_number | int |
| customer_number | int |
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Order_number是该表的主键。
此表包含关于订单ID和客户ID的信息。
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编写一个SQL查询，为下了 最多订单 的客户查找 customer_number 。
测试用例生成后， 恰好有一个客户 比任何其他客户下了更多的订单。
查询结果格式如下所示。
示例 1：
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| 输入:
Orders 表:
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| order_number | customer_number |
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| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 3 |
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输出:
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| customer_number |
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| 3 |
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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 。
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SQL结构
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| Create table If Not Exists orders (order_number int, customer_number int)
Truncate table orders
insert into orders (order_number, customer_number) values ('1', '1')
insert into orders (order_number, customer_number) values ('2', '2')
insert into orders (order_number, customer_number) values ('3', '3')
insert into orders (order_number, customer_number) values ('4', '3')
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解法1：
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| SELECT a.customer_number
FROM (
SELECT customer_number, COUNT(customer_number) order_count
FROM orders
GROUP BY customer_number) a
ORDER BY a.order_count DESC
LIMIT 1;
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官方解法：
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| SELECT customer_number
FROM orders
GROUP BY customer_number
ORDER BY COUNT(customer_number) DESC
LIMIT 1;
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原题链接：https://leetcode.cn/problems/customer-placing-the-largest-number-of-orders/