mysql中的unique keys

-- 创建单列唯一键
CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50) NOT NULL UNIQUE,
    email VARCHAR(100) NOT NULL UNIQUE
);

-- 创建复合唯一键
CREATE TABLE orders (
    order_id INT AUTO_INCREMENT PRIMARY KEY,
    user_id INT,
    product_id INT,
    order_date DATETIME,
    UNIQUE (user_id, product_id)
);

-- 使用INSERT IGNORE
INSERT IGNORE INTO users (username, email) VALUES ('testuser', 'test@example.com');

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

-- 分析索引
ANALYZE TABLE users;

-- 优化索引
OPTIMIZE TABLE users;