编辑代码

CREATE DATABASE test;
use test;
CREATE TABLE Orders (
	order_number int,
	customer_number int
);

INSERT INTO Orders VALUES (1,1);
INSERT INTO Orders VALUES (2,2);
INSERT INTO Orders VALUES (3,3);
INSERT INTO Orders VALUES (4,3);
select customer_number,count(*) 
as cn from Orders group by customer_number order by cn desc limit 1;