mysql_num_rows() not working at all - php

Question

I have this piece of PHP code:
<?php
$username=$_POST['username'];
$password=$_POST['password'];
if($username&&$password){
$connect=mysql_connect("localhost","root","") or die(" Couldnt connect");
mysql_select_db("phplogin") or die ("Can't find database" .mysql_error());
$query=mysql_query("SELECT * users WHERE username='$username' ");
$numrows=mysql_num_rows($query);
if (!$query) {
die('Invalid query: ' . mysql_error());
}
}
else
die ("Enter username and password!") .mysql_error();
?>
However, when I try to run this code I get these errors:
Warning: mysql_num_rows() expects parameter 1 to be resource, boolean given in C:\wamp\www\PHP testing\login.php on line 9
and
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'users WHERE username='alex'' at line 1
Can someone explain to me what I'm I doing wrong here?

Answer 1

You must specify a table from which you're selecting with FROM keyword:
$query=mysql_query("SELECT * FROM users WHERE username='$username' ");
$numrows=mysql_num_rows($query);

Answer 2

you should really check for errors after your query, then the system will tell you what is wrong
$query = mysql_query("SELECT * users WHERE username='$username' ");
if (mysql_error() {
die(mysql_error());
}
$numrows = mysql_num_rows($query);
as #mike commented, your select query is missing the from bit
"SELECT * FROM users WHERE username='$username' "

Answer 3

Well Your code is vulnerable to SQL Injection Attack
$username=$_POST['username'];
$password=$_POST['password'];
instead of above use this code
$username= mysql_real_escape_string($_POST['username']);
$password=mysql_real_escape_string($_POST['password']);

Answer 4

$connect = mysql_connect("localhost","root","") or die("Couldn't connect!");
mysql_select_db("phplogin") or die("Couldn't find db");
$result = mysql_query("SELECT * FROM admin", $connect);
$numrows = mysql_num_rows($result);
and it will evaluate resource

Answer 5

$query = mysql_query("SELECT * users WHERE username='$username' ");
if (mysql_error() {
die(mysql_error());
}
$numberOfRows = mysql_num_rows($query);
echo $numberOfRows;