<?php

$host = 127.0.0.1
$user = localhost
$password = ascent
$connection = mysql_connect($host, $user, $password)
or die("Connection to the database could not be established");
mysql_select_db("test") or die ("Database could not be selected");

$username = $_POST['username'];
$password = $_POST['password'];

$query = sprinft("SELECT username, password FROM userdb WHERE username='%s' AND password='%s'"",
    mysql_real_escape_string($username),
        mysql_real_escape_string($password));

$result = mysql_query($query);

if (!$result) {
    $message  = 'Invalid query: ' . mysql_error() . "\n";
    $message .= 'Whole query: ' . $query;
    die($message);
}