mysql表约束

-- 确保引用的主键存在
INSERT INTO orders (customer_id, order_date) VALUES (1, '2023-10-01');

-- 如果主键不存在，先插入主键数据
INSERT INTO customers (id, name) VALUES (1, 'John Doe');

-- 检查并删除重复数据
DELETE FROM users WHERE email = 'duplicate@example.com';

-- 再次插入数据
INSERT INTO users (email, name) VALUES ('duplicate@example.com', 'John Doe');

-- 修改数据以满足检查约束
UPDATE products SET price = 10 WHERE id = 1;

-- 创建表并添加约束
CREATE TABLE customers (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(100) NOT NULL,
    email VARCHAR(100) UNIQUE NOT NULL
);

CREATE TABLE orders (
    id INT AUTO_INCREMENT PRIMARY KEY,
    customer_id INT,
    order_date DATE,
    FOREIGN KEY (customer_id) REFERENCES customers(id)
);

-- 插入数据
INSERT INTO customers (name, email) VALUES ('John Doe', 'john.doe@example.com');
INSERT INTO orders (customer_id, order_date) VALUES (1, '2023-10-01');