mysql创建表 唯一约束条件

-- 创建单列唯一约束
CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50) NOT NULL UNIQUE,
    email VARCHAR(100) NOT NULL UNIQUE
);

-- 创建多列唯一约束
CREATE TABLE orders (
    order_id INT AUTO_INCREMENT PRIMARY KEY,
    user_id INT NOT NULL,
    order_number VARCHAR(50) NOT NULL,
    UNIQUE (user_id, order_number)
);

-- 示例：插入重复数据
INSERT INTO users (username, email) VALUES ('john_doe', 'john@example.com');

-- 如果username或email已经存在，会报错
INSERT INTO users (username, email) VALUES ('john_doe', 'john@example.com');

import mysql.connector

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