<?php

$q = "SELECT * FROM users WHERE username = '$username' AND password = '$password'";
$r = mysqli_query($dbc, $q) or die(mysqli_error($dbc));
if (mysqli_num_rows($r) == 1)
{
    $_SESSION['username'] = $username;
    echo '<script type="text/javascript">', 'LoginComplete();', '</script>';
}
else
{
    echo '<script type="text/javascript">', 'LoginError();', '</script>';
}