mysql_num_rows gives boolean error - authentication

Question

I'm working on a login script currently and I'm trying to get comfortable with query's and all those things around it. I'm getting it slightly, but the code below, which checks the username & password when people want to login, doesn't quite work. I get an error:
Warning: mysql_num_rows() expects parameter 1 to be resource, boolean given in C:\xampp\htdocs\mystagram\logic\login_validate.php on line 13
<?php
include('../includes/config.php');
include('../includes/database.php');
$username = mysql_escape_string($_POST['username']);
$password = mysql_escape_string($_POST['password']);
$submit = $_POST['submit_login'];
if (isset($submit)) {
$loginquery = mysql_query("SELECT * FROM users WHERE username='$username' AND password='$password'");
if (mysql_num_rows($loginquery) > 0) {
echo 'You are now logged in.';
exit();
} else {
echo 'Wrong username or password.';
}
}
?>

Answer 1

This means that you have an error in your SQL Statement.
Probably you dont have a table named 'users' or the Column 'username' or 'password' is missing.
Change this:
if (mysql_num_rows($loginquery) > 0) {
To:
if (mysql_num_rows($loginquery) == 1) {
And don't save your password in plaintext in the database. And use mysqli :)

Answer 2

you use mysql_escape_string() then '' it was problem. try this code,I hope it will work.
<?php
include('../includes/config.php');
include('../includes/database.php');
$username = mysql_escape_string($_POST['username']);
$password = mysql_escape_string($_POST['password']);
$submit = $_POST['submit_login'];
if (isset($submit)) {
**$loginquery = mysql_query("SELECT * FROM users WHERE username=".$username." AND password=".$password);**
if (mysql_num_rows($loginquery) > 0) {
echo 'You are now logged in.';
exit();
} else {
echo 'Wrong username or password.';
}
}
?>