使用 PHP 开发知识问答网站中的用户搜索历史和推荐功能。

CREATE TABLE `search_history` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `user_id` int(11) NOT NULL,
  `keyword` varchar(255) NOT NULL,
  `search_time` datetime NOT NULL,
  PRIMARY KEY (`id`),
  KEY `user_id` (`user_id`),
  KEY `keyword` (`keyword`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

// 假设用户已登录，获取用户ID
$user_id = $_SESSION['user_id'];

// 获取用户搜索关键词
$keyword = $_POST['keyword'];
$search_time = date('Y-m-d H:i:s');

// 将搜索历史插入数据库
$query = "INSERT INTO search_history (user_id, keyword, search_time) VALUES ('$user_id', '$keyword', '$search_time')";
mysqli_query($connection, $query);

// 获取当前用户的搜索历史
$query = "SELECT keyword FROM search_history WHERE user_id = '$user_id'";
$result = mysqli_query($connection, $query);

// 将搜索历史拼接为字符串，用于生成推荐内容
$search_history = '';
while ($row = mysqli_fetch_assoc($result)) {
  $search_history .= $row['keyword'] . ' ';
}

// 查询其他用户可能感兴趣的内容
$query = "SELECT keyword, COUNT(*) AS count FROM search_history WHERE user_id != '$user_id' AND keyword NOT IN ($search_history) GROUP BY keyword ORDER BY count DESC LIMIT 5";
$result = mysqli_query($connection, $query);

// 输出推荐内容
while ($row = mysqli_fetch_assoc($result)) {
  echo $row['keyword'] . '<br>';
}