表单验证不起作用

I want to display the error if user entered a duplicate name. But, it's not working. It keeps the name inserted even it's same. So, here is my code :

$namaErr = "";
$error==false;
if (isset($_POST['btnSubmit'])) {
if(isset ($_POST['nama'])){
$nama = $_POST['nama'];
$query ='SELECT nama FROM daftar_pengguna WHERE nama="' . $nama . '" LIMIT 
1';
$result = mysqli_query($query);
$totalNumRowResult = mysqli_num_rows($result);
if($totalNumRowResult > 0){
$error=true;
$namaErr="Nama ini telah digunakan!!";
} 
}

If no error, it will inserted in database :

else{
$query="INSERT INTO daftar_pengguna(nama) VALUES 
('$nama')";
$res = mysqli_query($query);
header('Location:index.php?registered=true');  
}    
}

I've searched all question like mine but, no luck.

I suggest two things:

1. Merge the if conditions to one block , this will remove the braces confusion had as I noted in above comment and also noted by Sujith.

2. Also I suggest you sanitize the $_POST variable before sending to Database query...

See code below with the suggested modifications:

<?php

$namaErr = "";
$error = false;

# Merge condition checks in One block using && (AND)
if (isset($_POST['btnSubmit']) && isset($_POST['nama'])) {

$nama = $_POST['nama'];

# Sanitize the input before running into Database query
$nama = filter_var($nama, FILTER_SANITIZE_STRING);


$query ='SELECT nama FROM daftar_pengguna WHERE nama="' . $nama . '" LIMIT 
1';
$result = mysql_query($query);
$totalNumRowResult = mysql_num_rows($result);

if($totalNumRowResult > 0){
  $error=true;
  $namaErr="Nama ini telah digunakan!!";
} 
else{
  $query="INSERT INTO daftar_pengguna(nama) VALUES ('$nama')";
  $res = mysql_query($query);
  header('Location:index.php?registered=true');  
}
}    

There was a problem with ther braces. This should work

$namaErr = "";
$error==false;
if (isset($_POST['btnSubmit'])) {
   if(isset ($_POST['nama'])){
      $nama = $_POST['nama'];
           $query ='SELECT nama FROM daftar_pengguna WHERE nama="' .$nama . '" LIMIT 1';
 $result = mysql_query($query);
 $totalNumRowResult = mysql_num_rows($result);
 if($totalNumRowResult > 0){
 $error=true;
 $namaErr="Nama ini telah digunakan!!";
  } 
 else{
    $query="INSERT INTO daftar_pengguna(nama) VALUES 
    ('$nama')";
    $res = mysql_query($query);
    header('Location:index.php?registered=true');  
    }    
    }
  }

try with this query :

$query ='SELECT nama FROM daftar_pengguna WHERE nama="' . $nama . '" ';