อยากได้คำชี้แนะวิธีแก้ Notice: Undefined index: form-username กับ Fatal error: Call to undefined function mysql_query()ค่ะ

<?php
include 'connect.php';
	@session_start();
if (!empty($_POST['submit'])) {
	header("Location:login.html");
	exit();
}
$test_query="SELECT * FROM login WHERE username = '".$_POST['form-username']."'";
$query_result=mysql_query($test_query) or die ($query .' '. mysql_error());
if(mysql_num_rows($query_result)==0) {
	echo "The username you entered is invalid.";
}else {
	while($row_query = mysql_fetch_array($query_result)){
		if($row_query['password']==$_POST['form-password']) {
			$_SESSION['password'] =$_POST['form-password'];
		header("Location:Home.php");
			exit();
	} else{
		echo "Password is not correct.";
	}
  }
}
?>