Validar.php

<?php
session_start();

$userdb = "";
$passdb = "";
$clientedb = "";

$conexion=mysqli_connect('localhost','root','','dark') or die ('Error al conectar con la base de datos');

    $consultau='select * from registros where user="'.$userdb.'"';
    $consultap='select * from registros where pass="'.$passdb.'"';
    $consultac='select * from registros where cliente="'.$clientedb.'"';

?>