تسجيل اكثر من مشترك بنفس ال username

مساء الخير افضل مبرمجين

ازاي امنع اكثر من عضو يسجل بنفس الuser name

استخدمت هذا الكود ولكن لم يمنع تسجيل بنفس user name 

وكود الphp 

<?php  
include('connect.php'); 
error_reporting(E_ALL^E_NOTICE);
if(isset($_POST['submit'])){   
	//-------username-------------//
	$wUserName=$_POST['wUserName'];  
	$sql="SELECT * FROM xuser WHERE wUserName='username'";
	$result = $conn->query($sql);  
	while ($row=$result->fetch_assoc()){
		$count=$result->num_rows;
	} 
		if($count >0){
		header('location:http://localhost/Artree/register0.php?q1=1'); 
		exit();
	} 
	 
	//-----------email-----------//
	$wEmail=$_POST['wEmail'];  
			if($count >0){
		header('location:http://localhost/Artree/register0.php?q3=3'); 
		exit();
	} 
	//----password-----------//
	$wPassword=$_POST['wPassWord']; 
	$wConfirmPassword=$_POST['wConfirmPassword']; 
	if($wPassword !==$wConfirmPassword){
		header('location:http://localhost/Artree/register0.php?q2=2'); 
		exit();
	} 
	//-----------------//
	$sql="INSERT INTO xuser(`wUserName`,`wEmail`,`wPassWord`, `wConfirmPassword`)
	VALUES('". $wUserName ."','" . $wEmail . "', '" . $wPassword . "','" . $wConfirmPassword ."')";
	$result = $conn->query($sql); 
} 
header('location:http://localhost/Artree/index.php')
 ?>

وهذا كود صفحه التسجيل

<div class="container">
	<div class="d-flex justify-content-center h-100">
		<div class="card">
			<div class="card-header">
				<h3>Registration</h3>
				</div>
			<div class="card-body"> 
			
				<form action="connect\Registeration.php" method="POST">
					<div class="input-group form-group">
						<div class="input-group-prepend">
							<span class="input-group-text"><i class="fa fa-user"></i></span>
						</div>
						<input type="text" class="form-control" placeholder="username" name="wUserName" required="">
						
					</div>
					<div class="input-group form-group">
						<div class="input-group-prepend">
							<span class="input-group-text"><i class="fa fa-envelope"></i></span>
						</div>
						<input type="Email" class="form-control" placeholder="Email" name="wEmail"required="">
					</div>
					<div class="input-group form-group">
						<div class="input-group-prepend">
							<span class="input-group-text"><i class="fa fa-key"></i></span>
						</div>
						<input type="Password" class="form-control" placeholder="Password"name="wPassWord"required="">
					</div>
                    
                     <div class="input-group form-group">
						<div class="input-group-prepend">
							<span class="input-group-text"><i class="fa fa-key"></i></span>
						</div>
						<input type="Confirm Password" class="form-control" placeholder="Confirm Password"name="wConfirmPassword" required="">
					</div>
					<div class="form-group">
                    <input type="submit" name="submit" value="Register Now"class="btn float-right sign_btn" >
					</div> 
                    
				</form>
			</div>
			<div class="card-footer">
				<div class="d-flex justify-content-center links">
					already have an account?<a href="login.php">Log in</a>
				</div>
				<div class="d-flex justify-content-center">
					<a href="passwordforget.php">Forgot your password?</a>
				</div>
			</div>
		</div>
	</div>
</div>