mysql连接查询多张表

-- 创建 users 表
CREATE TABLE users (
    user_id INT PRIMARY KEY,
    username VARCHAR(50),
    email VARCHAR(50)
);

-- 创建 orders 表
CREATE TABLE orders (
    order_id INT PRIMARY KEY,
    user_id INT,
    product_name VARCHAR(50),
    order_date DATE
);

-- 插入示例数据
INSERT INTO users (user_id, username, email) VALUES
(1, 'Alice', 'alice@example.com'),
(2, 'Bob', 'bob@example.com');

INSERT INTO orders (order_id, user_id, product_name, order_date) VALUES
(101, 1, 'Product A', '2023-01-01'),
(102, 2, 'Product B', '2023-01-02');

SELECT users.username, orders.product_name, orders.order_date
FROM users
INNER JOIN orders ON users.user_id = orders.user_id;

SELECT users.username, orders.product_name, orders.order_date
FROM users
LEFT JOIN orders ON users.user_id = orders.user_id;

SELECT users.username, orders.product_name, orders.order_date
FROM users
RIGHT JOIN orders ON users.user_id = orders.user_id;