问PHP:如何确保仅更新文本字段时不覆盖图像详细信息

EN

if (!empty($_FILES["image2"]))

  {
    $ed_author   = get_post($conn, 'ed_author');
    $ed_title    = get_post($conn, 'ed_title');
    $ed_category = get_post($conn, 'ed_category');
    $ed_year     = get_post($conn, 'ed_year');
    $hid_isbn     = get_post($conn, 'hid_isbn');

    $filetmp = $_FILES["image2"]["tmp_name"];
    $filename = $_FILES["image2"]["name"];
    $filetype = $_FILES["image2"]["type"];
    $filepath = "images/".$filename;

    move_uploaded_file($filetmp, $filepath);        

    $query    = "UPDATE classics SET author='$ed_author', title='$ed_title', type='$ed_category', year='$ed_year', filename='$filename', filepath='$filepath', filetype='$filetype'WHERE isbn='$hid_isbn'";     

    $result   = $conn->query($query);

    if (!$result) echo "EDIT with image failed: $query<br>" .
    $conn->error . "<br><br>";
    $result   = $conn->query($query);                   
  }
     else{
        $ed_author   = get_post($conn, 'ed_author');
        $ed_title    = get_post($conn, 'ed_title');
        $ed_category = get_post($conn, 'ed_category');
        $ed_year     = get_post($conn, 'ed_year');
        $hid_isbn     = get_post($conn, 'hid_isbn');
        $oldfilename = get_post($conn, 'oldfilename');
        $oldfilepath = get_post($conn, 'oldfilepath');
        $oldfiletype = get_post($conn, 'oldfiletype');      


    $query  = "UPDATE classics SET author='$ed_author', title='$ed_title', type='$ed_category', year='$ed_year', filename='$oldfilename', filepath='$oldfilepath', filetype='$oldfiletype' WHERE isbn='$hid_isbn'";     
        $result   = $conn->query($query);

    if (!$result) echo "EDIT with image failed: $query<br>" .
    $conn->error . "<br><br>";

     }   

 <form action="sqltest.php" method="post" enctype="multipart/form-data"><pre>
        Author <input type="text" name="ed_author" value="<?php echo $row[0]; ?>">
         Title <input type="text" name="ed_title" value="<?php echo $row[1]; ?>">
      Category <input type="text" name="ed_category" value="<?php echo $row[2]; ?>">
          Year <input type="text" name="ed_year" value="<?php echo $row[3]; ?>">
          ISBN <input type="text" name="hid_isbn" value="<?php echo $row[4]; ?>"readonly>

               <input type="hidden" name="oldfilename" value="<?php echo $row[6]; ?>">  
               <input type="hidden" name="oldfilepath" value="<?php echo $row[7]; ?>">
               <input type="hidden" name="oldfiletype" value="<?php echo $row[8]; ?>">

               <input type="file" name="image2">
               <input type="hidden" name="edit" value="yes">
               <input type="submit" name="btn2" value="SUBMIT EDIT">

        </pre></form>