<?php
global $tainted;
$tainted = 'Constant';

$GLOBALS['tainted'] = 'Constant';
$GLOBALS['tainted'] = $_POST['TaintedData'];

$db = mysqli_connect("127.0.0.1", "root", "123456");
mysqli_select_db($db, "testcasesqli");
$query = "select * from users where id=$GLOBALS['tainted']";
$result = mysqli_query($db, $query);
if ($result == false) {
    exit("Database error !<br />");
}
$row = mysqli_fetch_array($result);
if ($row == null) {
    exit("Error ID or password.<br />");
}
print("Login successfully!<br />welcome,".$row[1]."<br />");