mysql重复写入数据

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(255) NOT NULL UNIQUE,
    email VARCHAR(255) NOT NULL UNIQUE
);

import mysql.connector

def insert_user(username, email):
    conn = mysql.connector.connect(user='user', password='password', host='host', database='database')
    cursor = conn.cursor()
    
    # 检查用户是否存在
    cursor.execute("SELECT * FROM users WHERE username = %s OR email = %s", (username, email))
    result = cursor.fetchone()
    
    if result:
        print("User already exists")
    else:
        cursor.execute("INSERT INTO users (username, email) VALUES (%s, %s)", (username, email))
        conn.commit()
    
    cursor.close()
    conn.close()

START TRANSACTION;
SELECT * FROM users WHERE username = 'unique_username' FOR UPDATE;
-- 如果没有找到记录，则插入数据
INSERT INTO users (username, email) VALUES ('unique_username', 'unique_email');
COMMIT;