如何檢查文件是否已上傳在php codeigniter

Question

我必須上傳文件並將數據插入到表格中。我已完成該部分。 現在，我想檢查文件是否已經上傳或不。如果是這樣，應該拋出警報。

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{ 
        }