php - MySQLi Login - Get no errors but nothing happens -

i'm sure following line wrong:

if ($mquery){ 

since num_rows won't work, i'm using it.
if condition wrong, should change for?

php login code:

<?php     $mysqli = mysqli_connect("localhost","myuser","mypass","mydb");     $error = false;      $mquery = $mysqli->query('select * usuarios usuario = '.$mysqli->real_escape_string(md5($_post['usuario'])).' ,  senha = '.$mysqli->real_escape_string(md5($_post['senha'])));      if ($mquery){         $majax = (isset($_server['http_x_requested_with']) , strtolower($_server['http_x_requested_with']) == 'xmlhttprequest');         if ($majax)         {             header('cache-control: no-cache, must-revalidate');             header('expires: '.date('r', time()+(86400*365)));             header('content-type: application/json');              echo json_encode(array(             'logged' => !$error             ));             exit();         }         elseif (!$error)         {             exit();         }     } ?> 

try change query from

$mquery = $mysqli->query('select * usuarios usuario = '.$mysqli->real_escape_string(md5($_post['usuario'])).' ,  senha = '.$mysqli->real_escape_string(md5($_post['senha']))); 

to

$mquery = $mysqli->query("select * usuarios usuario = '" .            $mysqli->real_escape_string(md5($_post['usuario'])) .            "' ,  senha = '" .            $mysqli->real_escape_string(md5($_post['senha'])) . "'");