mysql创建主外键关联

CREATE TABLE customers (
    customer_id INT AUTO_INCREMENT PRIMARY KEY,
    customer_name VARCHAR(100) NOT NULL,
    email VARCHAR(100) UNIQUE NOT NULL
);

CREATE TABLE orders (
    order_id INT AUTO_INCREMENT PRIMARY KEY,
    order_date DATE NOT NULL,
    customer_id INT,
    FOREIGN KEY (customer_id) REFERENCES customers(customer_id)
);

-- 插入主键表数据
INSERT INTO customers (customer_name, email) VALUES ('John Doe', 'john.doe@example.com');

-- 插入外键表数据
INSERT INTO orders (order_date, customer_id) VALUES ('2023-10-01', 1);

CREATE TABLE orders (
    order_id INT AUTO_INCREMENT PRIMARY KEY,
    order_date DATE NOT NULL,
    customer_id INT,
    FOREIGN KEY (customer_id) REFERENCES customers(customer_id) ON DELETE CASCADE
);

CREATE TABLE orders (
    order_id INT AUTO_INCREMENT PRIMARY KEY,
    order_date DATE NOT NULL,
    customer_id INT,
    FOREIGN KEY (customer_id) REFERENCES customers(customer_id) ON DELETE SET NULL
);