sql notes: leetcode#586 customer placing the largest number of orders

Problem

Query the customer_number from the orders table for the customer who has placed the largest number of orders.

It is guaranteed that exactly one customer will have placed more orders than any other customer.

The orders table is defined as follows:

Sample Input

Sample Output

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’.

Analysis

• Output customer_number from table orders:

1

SELECT customer_number FROM orders;

• Group by customer_number and count number of orders for each group. Then sort groups by each group’s number of orders in descending order:

1

SELECT customer_number FROM orders GROUP BY customer_number ORDER BY COUNT(*) DESC;

• Use limit to output the first row:

1

SELECT customer_number FROM orders GROUP BY customer_number ORDER BY COUNT(*) DESC LIMIT 1;

Solution

1

SELECT customer_number FROM orders GROUP BY customer_number ORDER BY COUNT(*) DESC LIMIT 1;

Link

586. Customer Placing the Largest Number of Orders
(中文版) SQL 笔记: Leetcode#586 Customer Placing the Largest Number of Orders