mysql数据库别名使用查询

CREATE TABLE employees (
    id INT PRIMARY KEY,
    name VARCHAR(100),
    department_id INT
);

CREATE TABLE departments (
    id INT PRIMARY KEY,
    name VARCHAR(100)
);

SELECT e.name AS employee_name, d.name AS department_name
FROM employees e
JOIN departments d ON e.department_id = d.id;

SELECT name AS employee_name, department_id
FROM employees;

-- 错误示例
SELECT e.name AS employee_name, d.name AS department_name
FROM employees e
JOIN departments d ON e.department_id = d.id;

-- 正确示例
SELECT e.name AS employee_name, d.name AS department_name
FROM employees AS e
JOIN departments AS d ON e.department_id = d.id;

SELECT e.id AS employee_id, d.id AS department_id
FROM employees e
JOIN departments d ON e.department_id = d.id;