如何保存在数据库中只有“完整”的唯一对象？

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50) NOT NULL,
    email VARCHAR(100) NOT NULL UNIQUE,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

INSERT INTO users (username, email) VALUES ('user1', 'user1@example.com');
-- 尝试插入重复的电子邮件地址将会失败
INSERT INTO users (username, email) VALUES ('user2', 'user1@example.com'); -- 这将引发错误

import mysql.connector

try:
    conn = mysql.connector.connect(user='your_user', password='your_password', host='your_host', database='your_database')
    cursor = conn.cursor()
    cursor.execute("INSERT INTO users (username, email) VALUES (%s, %s)", ('user3', 'user3@example.com'))
    conn.commit()
except mysql.connector.IntegrityError as e:
    print(f"Error: {e}")
finally:
    cursor.close()
    conn.close()