Help Needed

hi, I have started working with PHP-MySQL recently. I have been getting a warning message which i am not able to debug. Could some one pls help me out? The message is Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in /usr/local/apache2/htdocs/verify.php on line 37 The code is

      @$db=mysql_pconnect("localhost:/var/lib/mysql/mysql.sock","","");

      if(!$db)
      {
       echo " The Server is Busy. Please Try Later ";
       exit;
      }

     mysql_select_db("userinfo");

     $query = "select * from userinfo";

     $mysql_results = mysql_query($query,$db);

line 37:$num_result = mysql_num_rows($mysql_results);

     if($num_result == 0)
      {
        echo "<P>Invalid Username or Password entered</P>";
        exit;
      }

Regards, Manoj 'I have miles to go before I sleep, and promises to keep'