mysql 建立表外键约束

-- 创建 customers 表
CREATE TABLE customers (
    customer_id INT PRIMARY KEY AUTO_INCREMENT,
    customer_name VARCHAR(100) NOT NULL
);

-- 创建 orders 表，并添加外键约束
CREATE TABLE orders (
    order_id INT PRIMARY KEY AUTO_INCREMENT,
    order_date DATE NOT NULL,
    customer_id INT,
    FOREIGN KEY (customer_id) REFERENCES customers(customer_id)
        ON DELETE CASCADE
        ON UPDATE CASCADE
);

-- 禁用外键约束
SET FOREIGN_KEY_CHECKS = 0;

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

-- 启用外键约束
SET FOREIGN_KEY_CHECKS = 1;

-- 禁用外键约束
SET FOREIGN_KEY_CHECKS = 0;

-- 更新数据
UPDATE orders SET customer_id = 2 WHERE order_id = 1;

-- 启用外键约束
SET FOREIGN_KEY_CHECKS = 1;