mysql 设置唯一值

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

INSERT INTO users (username, email) VALUES ('user1', 'user1@example.com');
INSERT INTO users (username, email) VALUES ('user2', 'user2@example.com');

INSERT INTO users (username, email) VALUES ('user1', 'user1@example.com'); -- 会报错，因为username和email都是唯一的

INSERT INTO users (username, email) VALUES ('user1', 'user1@example.com')
ON DUPLICATE KEY UPDATE email = 'user1@example.com';

DELETE FROM users WHERE username = 'user1' OR email = 'user1@example.com';
INSERT INTO users (username, email) VALUES ('user1', 'user1@example.com');