customer-placing-the-largest-number-of-orders

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Database

Table: <code>Orders</code>

<pre>
+-----------------+----------+
| Column Name | Type |
+-----------------+----------+
| order_number | int |
| customer_number | int |
+-----------------+----------+
order_number is the primary key (column with unique values) for this table.
This table contains information about the order ID and the customer ID.
</pre>

&nbsp;

Write a solution to find the <code>customer_number</code> for the customer who has placed the largest number of orders.

The test cases are generated so that exactly one customer will have placed more orders than any other customer.

The result format is in the following example.

&nbsp;
Example 1:

<pre>
Input: 
Orders table:
+--------------+-----------------+
| order_number | customer_number |
+--------------+-----------------+
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 3 |
+--------------+-----------------+
Output: 
+-----------------+
| customer_number |
+-----------------+
| 3 |
+-----------------+
Explanation: 
The customer with number 3 has two orders, which is greater than either customer 1 or 2 because each of them only has one order. 
So the result is customer_number 3.
</pre>

&nbsp;
Follow up: What if more than one customer has the largest number of orders, can you find all the <code>customer_number</code> in this case?

largest_orders

Customer Placing the Largest Number of Orders

表:&nbsp;<code>Orders</code>

<pre>
+-----------------+----------+
| Column Name | Type |
+-----------------+----------+
| order_number | int |
| customer_number | int |
+-----------------+----------+
在 SQL 中，Order_number是该表的主键。
此表包含关于订单ID和客户ID的信息。
</pre>

&nbsp;

查找下了 最多订单&nbsp;的客户的 <code>customer_number</code> 。

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。

&nbsp;

示例 1:

<pre>
输入: 
Orders 表:
+--------------+-----------------+
| order_number | customer_number |
+--------------+-----------------+
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 3 |
+--------------+-----------------+
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 。
</pre>

&nbsp;

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 <code>customer_number</code> 吗？