mysql设置主键和外键

-- 创建用户表
CREATE TABLE users (
    user_id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50) NOT NULL,
    email VARCHAR(100) NOT NULL UNIQUE
);

-- 创建订单表
CREATE TABLE orders (
    order_id INT AUTO_INCREMENT PRIMARY KEY,
    user_id INT NOT NULL,
    order_date DATE NOT NULL,
    FOREIGN KEY (user_id) REFERENCES users(user_id)
);

-- 查询所有订单及其对应的用户信息
SELECT orders.order_id, orders.order_date, users.username, users.email
FROM orders
JOIN users ON orders.user_id = users.user_id;

-- 禁用外键检查
SET FOREIGN_KEY_CHECKS = 0;

-- 插入数据
INSERT INTO orders (user_id, order_date) VALUES (1, '2023-10-01');

-- 启用外键检查
SET FOREIGN_KEY_CHECKS = 1;

-- 使用自增主键
CREATE TABLE users (
    user_id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50) NOT NULL,
    email VARCHAR(100) NOT NULL UNIQUE
);