функция strtolower для Логина

<?php
 
session_start();
 
$username = $_POST["username"];
$password = $_POST["password"];
 
if ($username&&$password)
{
 
$connect = mysql_connect ("sale00.mysql.ukraine.com.ua","sale00_db","123456") or die("Couldn't connect!");
mysql_select_db ("sale00_db",$db) or die ("Couldn't find db");
 
$query = mysql_query("SELECT * FROM `Users` WHERE username='$username'");
 
$numrows = mysql_num_rows($query);
 
if ($numrows!=0)
{
 
while ($row = mysql_fetch_assoc($query))
{
$dbusername = $row["username"];
$dbpassword = $row["password"]; 
}
 
//check to see if they match!
if ($username==$dbusername&&($password)==$dbpassword)
{
echo "You're in! <a href='member.php'>Click</a> here to enter the member page.";
$_SESSION["username"]=$username;    
}
else
    echo "Incorrect password!";
}
else
    die("That user doesn't exist!");
 
    
}
else
    die("Please enter and username and a password!");
 
 
?>

$username = strtolower($username);

$query = mysql_query("SELECT * FROM `Users` WHERE username = strtolower($username);

$username = $_POST["strtolower($username)"];

$_SESSION["username"]=strtolower($username);

$username = strtolower($username);

$username = strtolower($_POST["username"]);