leetcode - 586. Customer Placing the Largest Number of Orders

난이도 : Easy

 

Table: Orders

+-----------------+----------+
| Column Name     | Type     |
+-----------------+----------+
| order_number    | int      |
| customer_number | int      |
+-----------------+----------+
order_number is the primary key for this table.
This table contains information about the order ID and the customer ID.

 

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 Orders
GROUP BY customer_number
HAVING COUNT(order_number)
ORDER BY COUNT(order_number) DESC
LIMIT 1

Accepted (24.33%)

 

 

SELECT customer_number
FROM Orders
GROUP BY customer_number
HAVING COUNT(order_number) = (
                              SELECT COUNT(*) cnt
                              FROM Orders
                              GROUP BY customer_number
                              ORDER BY cnt DESC
                              LIMIT 1
                              )

Accepted (25.61%)

 

 

윈도우 함수를 활용한 방법

WITH sub2 AS (
              SELECT customer_number
                   , DENSE_RANK() OVER (ORDER BY cnt DESC) rnk
              FROM (SELECT customer_number
                         , COUNT(order_number) cnt
                    FROM Orders
                    GROUP BY customer_number) sub
              )
SELECT customer_number
FROM sub2
WHERE rnk = 1

Accepted (38.26%)