SELECT department_id, employee_name, AVG(salary)
FROM employees
GROUP BY department_id;

SELECT department_id, employee_name, AVG(salary)
FROM employees
GROUP BY department_id;

-- 设置SQL模式为ONLY_FULL_GROUP_BY
SET sql_mode = 'ONLY_FULL_GROUP_BY';

-- 或修改my.cnf/my.ini文件永久生效
[mysqld]
sql_mode=ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION

-- 正确写法(两者都兼容)
SELECT department_id, MAX(employee_name) as employee_name, AVG(salary)
FROM employees
GROUP BY department_id;

-- 或
SELECT e.department_id, e.employee_name, e.salary
FROM employees e
JOIN (
    SELECT department_id, AVG(salary) as avg_salary
    FROM employees
    GROUP BY department_id
) dept_avg ON e.department_id = dept_avg.department_id;