如果缺少最新数据，则添加行

-- 示例：使用唯一约束
CREATE TABLE IF NOT EXISTS user_activity (
    id INT AUTO_INCREMENT PRIMARY KEY,
    user_id INT NOT NULL,
    activity_type VARCHAR(50) NOT NULL,
    activity_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    UNIQUE (user_id, activity_type, activity_time)
);

-- 示例：使用事务和锁
START TRANSACTION;
SELECT * FROM user_activity WHERE user_id = 1 AND activity_type = 'login' FOR UPDATE;
INSERT INTO user_activity (user_id, activity_type) VALUES (1, 'login');
COMMIT;

-- 示例：批量插入
INSERT INTO user_activity (user_id, activity_type)
SELECT 1, 'login' FROM DUAL
WHERE NOT EXISTS (
    SELECT 1 FROM user_activity WHERE user_id = 1 AND activity_type = 'login' ORDER BY activity_time DESC LIMIT 1
);