mysql 数据库外键约束

-- 创建主键表
CREATE TABLE customers (
    customer_id INT PRIMARY KEY,
    customer_name VARCHAR(100)
);

-- 创建外键表
CREATE TABLE orders (
    order_id INT PRIMARY KEY,
    customer_id INT,
    order_date DATE,
    FOREIGN KEY (customer_id) REFERENCES customers(customer_id)
);

-- 插入数据
INSERT INTO customers (customer_id, customer_name) VALUES (1, 'Alice');
INSERT INTO orders (order_id, customer_id, order_date) VALUES (101, 1, '2023-04-01');

-- 尝试插入无效数据
INSERT INTO orders (order_id, customer_id, order_date) VALUES (102, 2, '2023-04-02'); -- 这将失败，因为customer_id 2不存在

-- 创建外键表并设置级联删除
CREATE TABLE orders (
    order_id INT PRIMARY KEY,
    customer_id INT,
    order_date DATE,
    FOREIGN KEY (customer_id) REFERENCES customers(customer_id) ON DELETE CASCADE
);

-- 删除客户数据，级联删除订单数据
DELETE FROM customers WHERE customer_id = 1;