​LeetCode刷题实战586：订单最多的客户

Write an SQL query to find the customer_number 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.

select customer_number from (
  select
    customer_number,
    dense_rank() over(order by count(*) desc) as rn
  from orders group by customer_number
) temp where rn = 1;