我不是最熟练的开发人员，但是我和我的朋友们为一个项目组织起来，创建了一个植物自动浇水系统。我的职责是让网站工作并显示系统创建的统计数据。
在从csv文件添加新数据之前，如何让代码清除表？
以下是索引页上显示的代码：

<!-- Importing the CSV -->

        <div id="wrap">
        <h2 class='sub-header'>Upload .csv to refresh data</h2>
          <?php
            include("csv.php");
            $csv = new csv();
            if ( isset($_POST['sub'])) {
              $csv->import($_FILES['file']['tmp_name']);
            }
          ?>

          <form method="post" enctype="multipart/form-data">
            <input type="file" name="file" class="btn btn-info"><br>
            <input type="submit" name="sub" value="Import" class="btn btn-success"> 
          </form>
        </div>
      </div>
    </div>

以下是php文件：

<?php
class csv extends mysqli
{
    private $state_csv = false;
    public function __construct()
    {
        parent::__construct("localhost","root","raspberry","statistics");
        if ($this->connect_error) {
            echo "Failed to connect to the database: ". $this->connect_error;
        }
    }
    public function import($file)
    {
        $file = fopen($file, 'r');
        while ($row = fgetcsv($file)) {
            $value = "'". implode("','", $row) ."'";
            $q = "INSERT INTO data(moisture_of_soil,temperature,humidity,light_levels,last_updated) VALUES(". $value .")";
            if ( $this->query($q) ) {
                $this->state_csv = true;
            }else {
                $this->state_csv = false;
            }
        }
        if ($this->state_csv) {
            echo "<meta http-equiv='refresh' content='0'>";
        } else {
            echo "Something went wrong.";
        }
    }
}
?>