如何在mysql中组合内部和外部联接

-- 创建 employees 表
CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(255),
  department_id INT
);

-- 创建 departments 表
CREATE TABLE departments (
  id INT PRIMARY KEY,
  name VARCHAR(255)
);

-- 向 employees 表插入数据
INSERT INTO employees (id, name, department_id)
VALUES (1, 'John Doe', 1),
       (2, 'Jane Smith', 2),
       (3, 'Bob Johnson', 1);

-- 向 departments 表插入数据
INSERT INTO departments (id, name)
VALUES (1, 'Sales'),
       (2, 'Marketing'),
       (3, 'IT');

-- 内部联接
SELECT employees.id, employees.name, departments.name
FROM employees
JOIN departments ON employees.department_id = departments.id;

-- 外部联接
SELECT employees.id, employees.name, departments.name
FROM employees
LEFT JOIN departments ON employees.department_id = departments.id
UNION
SELECT employees.id, employees.name, departments.name
FROM employees
RIGHT JOIN departments ON employees.department_id = departments.id;