php中的EDIT/DELETE帖子出现意外错误

首先，很抱歉代码太长，但我认为它很重要。所有这些都是关于编辑和删除我页面上的新闻。但我不知道为什么它说：语法错误，意外的（最后）等等。有人能帮我摆脱困境吗？此外，当我试图删除其他内容以了解会出现什么时，它没有显示任何内容。只有CSS样式的背景，但没有其他类似的形式等。。

  <?php
          $servername = "localhost";
          $username = "u296093122_admin";
          $password = "a";
          $dbname = "u296093122_datab";

        if(isset($a)){
            $conn = new mysqli($servername, $username, $password, $dbname);
          if ($conn->connect_error) {
           die("->Pripojenie neúspešné: " . $conn->connect_error);
                                    }
            $sql = "SELECT id, nadpis, timestamp FROM Akcie ORDER BY timestamp DESC";
            $result = $conn->query($sql);
        if (mysql_num_rows($result) > 0){
            while($row = mysql_fetch_object($result))
                {
    ?>
 <font size="-1"><b><?php echo $row->nadpis; ?></b> <i><?php echo $row->timestamp; ?></i></font>
<br>
  <font size="-2"><a href="edit.php?a=edit&id=<?php echo $row->id; ?>">upraviť</a> | 
  <a href="edit.php?a=delete&id=<?php echo $row->id; ?>">vymazať</a></font>
<?php
    }
?>
 <font size="-2">No news in the database</font>
<?php
    }
mysql_close($conn);
    }elseif($a == 'edit'){
        if(!isset($update)){
    $conn = new mysqli($servername, $username, $password, $dbname);
    $sql = "SELECT nadpis, obsah FROM Akcie WHERE id = '$id'";
    $result = $conn->query($sql);
mysql_fetch_object($result);
?>
 <form name="form2" method="post" action="edit.php?a=edit&id=<?php echo($id) ?>&update=1">
 <table width="50%" border="0" cellspacing="0" cellpadding="0">
  <tr> 
  <td>Nadpis</td>
  <td><input name="nadpis" type="text" id="nadpis" value="<?php echo($row->nadpis) ?>"></td>
</tr>
<tr> 
  <td>Obsah</td>
  <td><textarea name="obsah" id="obsah" value="<?php echo($row->obsah) ?>"></textarea></td>
</tr>
<tr> 
  <td colspan="2"><div align="center">
      <input name="hiddenField" type="hidden" value="update">
      <input name="add" type="submit" id="add" value="Update">
    </div></td>
</tr>
</table>
</form>
 <?php
}else{
    $sql = "UPDATE Akcie SET nadpis = '$nadpis', obsah = '$obsah', timestamp = NOW() WHERE id = '$id'";
    $result = $conn->query($sql);
    if(!$result){
        echo('Error updating news item: ' . $mysql_error());
        exit();
    }else{
        mysql_close($conn);
        echo('Update successful!');
        }
    } }elseif($a == 'delete'){
        $conn = new mysqli($servername, $username, $password, $dbname);
    $sql = "DELETE FROM Akcie WHERE id = '$id'";
    $result = $conn->query($sql);

    if(!$result){
        echo('Error deleteing news item: ' . $mysql_error());
         exit();
            }
    mysql_close($conn);
    echo('News item deleted.');
    }
     ?>