AJAX update and delete error but still successful error - php

Question

**
I have a problem when updating and deleting, when I incorrectly enter the column id, although the database does not change, the system still reports
success **
$loai = trim($_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");
}