MySQL当同一表中有一个或多个相同的信息时，如何选择/列出数据名？

Question

create database Exercise;

use Exercise;

create table Employee (
    employee_id int(5), 
    employee_name varchar(30), 
    join_date date
);

create table Customer (
    customer_id int(5), 
    customer_name varchar(30), 
    cust_join_date date default '2012-12-06', 
    employee_id int(5)
);

alter table Employee add constraint pk__emp primary key(employee_id);
alter table Customer add constraint pk__cust primary key(customer_id);
alter table Customer add constraint fk__cust foreign key(employee_id) references employee(employee_id);
alter table Employee add (emp_age int(3),emp_gender char(1));
alter table Customer modify column customer_name varchar(1000);

insert into Employee values (0001,'Aabrara','2014-02-01',20,'M');
insert into Employee values (0002,'Babara','2015-02-02',21,'F');
insert into Employee values (0003,'Crabrara','2015-02-03',30,'F');
insert into Employee values (0004,'Drabara','2014-02-04',23,'M');
insert into Employee values (0005,'Earbrara','2014-02-05',28,'F');

insert into Customer values (1000,'Fabara','2015-02-06',0001);
insert into Customer values (2000,'Gabare','2015-02-07',0002);
insert into Customer values (3000,'Habari','2015-02-08',0002);
insert into Customer values (4000,'Iabaro','2015-02-09',0004);
insert into Customer values (5000,'Jabaru','2015-02-10',0005);

上面是表格，问题是‘查找员工id和员工名称谁正在处理多个客户’。怎么做？！我被告知要使用子查询，但我仍然无法解决它。

Answer 1

SELECT `Employees`.`employee_id`, `Employees`.`employee_name`
FROM `Employees`
INNER JOIN `Customers` USING (`employee_id`)
GROUP BY `Employees`.`employee_id`
HAVING (COUNT(`Customers`.`customer_id`) > 1)
ORDER BY `Employees`.`employee_name`