<?php
error_reporting(E_ALL);
$username = $_REQUEST["username"]; 
$password = $_REQUEST["password"];
$database = (isset($_REQUEST["database"]) ? $_REQUEST["database"] : null);

$link = mysqli_connect("localhost", $username, $password, $database);
if (!$link) {
  die("Error connecting to mysql: " . mysqli_connect_error() . " (" . mysqli_connect_errno() . ")");
}

$res = mysqli_query($link, $_REQUEST["query"]);
if (!$res) {
  die("Error executing query: " . mysqli_error($link));
}

while ($row = $res->fetch_assoc()) {
  var_dump($row);
}

mysqli_close($link);
?>