mysql中防止重复的属性

ERROR 1062 (23000): Duplicate entry 'example@example.com' for key 'email'

-- INSERT IGNORE
INSERT IGNORE INTO users (email, name) VALUES ('example@example.com', 'John Doe');

-- ON DUPLICATE KEY UPDATE
INSERT INTO users (email, name) VALUES ('example@example.com', 'John Doe')
ON DUPLICATE KEY UPDATE name = 'John Doe';

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

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

ALTER TABLE users ADD UNIQUE (email);