AJAX更新和删除错误，但仍然成功

Question

** 我更新和删除时遇到问题，当我输入错误的列ID时，尽管数据库没有更改，但系统仍会报告 成功**

$loai = trim($_POST['loai']);
 $id = trim($_POST['id']);
    $ten = trim($_POST['ten']);
    $idghichu = trim($_POST['idghichu']);
$sql;
$conn = new mysqli('localhost','root','12345678','chamcomvantay');
if($loai == "xoa") {
$sql = "DELETE FROM chamcomvantay.tb_bophan WHERE ID='$id' ";
 }
elseif ($loai == "sua") {
    $sql = "UPDATE chamcomvantay.tb_bophan SET TENBP='$ten', GHICHU='$idghichu' WHERE ID='$id'   ";
}
if(mysqli_query($conn, $sql)) {

echo "success";    // This is an error //

 } else {
  echo "Lỗi";
}

$conn->close();
?>

--my ajax code---- 

$idbophan  = $('#idbophan').val();   
$idten =  $('#idten').val();
$idghichu = $('#idghichu').val();
$loai = "sua";
if($idbophan.trim() != "" ){
$.post('thaotacbophan.php',{'id':$idbophan.trim(),'ten': $idten.trim(),'idghichu':$idghichu.trim(),'loai':$loai.trim()}, function(data){
alert(data); // error but still alert("success"); ///
  });
}
else{
  alert("Vui lòng điền đầy đủ thông tin");
}