如何检查文件是否已经上传到php codeigniter中

Question

我必须上传一个文件并将数据插入tables.i我已完成该部分。 现在，我想检查文件是否已经上传。如果是这样，应该抛出警报。

    if(isset($_POST["submit"]))
    {
    if($_FILES['file']['name'])
    {
        $filename = explode(".", $_FILES['file']['name']);
        $a=$filename[0];
        foreach($a as $b){
        if($b==$filename[0]){
                            echo"file already uploaded";
                            }
                          }
     }
   }

Answer 1

             if($filename[1] == 'csv')
                                    {

                                         $fp = fopen($_FILES['file']['tmp_name'],'r') or die("can't open file");
                                         $a=$filename[0];
                                         echo $a;
                                         $query1 = $this->db->query("SELECT * from table WHERE table.filename='".$a."'");
                                         $b=$query1->num_rows();
                                         if($b>0)

                                         {
                                            echo "<script type='text/javascript'>alert('FILE ALREADY BEEN UPLOADED')</script>";
                                         }
              else{
                  }