Why is mysql_num_rows() returning 0? - php

Question

I have read in another threads that pasting the query in phpMyAdmin returns the amount of rows that you have, but in my case it doesn't even returns a value in phpMyAdmin, it's always 0! Here is the query:
$query = "SELECT nom_usu FROM usuarios WHERE nom_usu = '$usu' AND pass = '$pass';";
I open the .php file and run the query and it returns empty values, like this:
SELECT nom_usu FROM usuarios WHERE nom_usu = '' AND pass = '';
I also tried to echo the value that returns and is, guess what? Zero!
Here is the complete .php file (is for a login):
<?php
include('dbConfig.php');
$usu = $_POST["usu"];
$pass = $_POST["pass"];
$query = "SELECT nom_usu FROM usuarios WHERE nom_usu = '$usu' AND pass = '$pass';";
echo $query."\n";
if($resultado = mysql_query($query)){
if(mysql_num_rows($resultado) > 0){
echo mysql_num_rows($resultado);
echo "Todo está bien, no te preocupes :)";
echo true;
} else {
echo mysql_num_rows($resultado);
echo "Hay algo mal aquí :(";
}
} else {
echo false;
}
?>
And the dbConfig.php file:
<?php
$host="localhost";
$user="neosoftw_lambda";
$contra="myPass"; <- This is not actually my password...
$db="neosoftw_lambdaMovil";
$ms = mysql_connect($host, $user, $contra) or die("No se pudo conectar :(");
mysql_select_db($db, $ms) or die ("No hay base de datos :(");
?>
Hope someone can help me figure out where I have gone wrong?
Here is what I want to make, is a login in jQuery Mobile, but it doesn't work!
Username: bryan
Password: azul
http://android.neosoftware.org.mx/
Edit
Maybe it could be because of my javascript?
$.post("http://android.neosoftware.org.mx/PHP/login.php", {usu : usu, pass : pass}, function(respuesta_login){
if(!($("#txt_usuario").val() || $("#txt_password") == '')){
$.mobile.changePage("#campos_vacios");
} else {
if(respuesta_login == 1){
$("#txt_usuario").val('');
$("#txt_password").val('');
$.mobile.changePage("#pag_principal");
} else {
$.mobile.changePage("#error_login");
}
}
});

Answer 1

Use mysqli or PDO statements, as mysql is deprecated. Try this:
$usu = mysqli_real_escape_string($_POST["usu"]);
$pass = mysqli_real_escape_string($_POST["pass"]);
$query = "SELECT nom_usu FROM usuarios WHERE nom_usu = '".$usu."' AND pass = '".$pass."'";
And also your condition is incorrect.It should be like this:
if($resultado == mysqli_query($query)){

Answer 2

Try this query.
$query = "SELECT `nom_usu` FROM usuarios WHERE `nom_usu` = '".$usu."' AND `pass` = '".$pass."'";
Also this type of problem occurre when $_POST variable is empty.. So, double check your code.
Note : mysql_* function is deprecated, move on mysqli_* function asap.