Session variables not being transported - php

Question

I'm learnig PHP (as a hobby) and I wanted to build a simple login page to practice.
I have a form:
<form action="phpAction/checklogin.php" method="POST">
<p>Username:</p>
<input type="text" name="username">
<p>Password:</p>
<input type="password" name="password">
<br><br>
<input type="submit" value="Submit">
<br><br>
You don't have an account yet?
</form>
Posting to the php code:
<?php
// Starts a MySQLi connection to the database
include "../includes/mysqliConn.php";
// Starts a session to keep the user logged in
session_start();
// Posts the username and password from the form and stores it into a session variable
if (isset($_POST["username"]) && isset($_POST["password"])) {
$_SESSION["username"] = $_POST["username"];
$_SESSION["password"] = $_POST["password"];
} else {
die("You cannot be here!");
}
// Checks login
$checklogin = 'SELECT * FROM users WHERE username = $_SESSION["username"] AND password = $_SESSION["password"]';
$result = $conn->query($checklogin);
if ($result->num_rows = 0){
echo "<script language='javascript' type='text/javascript'>alert('Login and/or password wrong!');window.location.href='login.php';</script>";
die();
} else {
// Variable to other pages see that the user is logged in
$_SESSION["islogged"] = "true";
// Redirects to the homepage
header("Location: ../index.php");
}
?>
It sets the session variable "islogged" to true so that other pages can diplay user's information.
In the header of the website I have this:
<?php
if ($_SESSION["islogged"] == "true") {
echo "<a href='#'>Panel</a>";
echo "<a href='#'>Logout</a>";
} else {
echo "<a href='login.php'>Login</a>";
echo "<a href='#'> / </a>";
echo "<a href='signup.php'>Sign Up</a>";
}
?>
When the variable "islogged" is set to "true", the page should display the links Panel and Logout, instead of the Login and Signup ones. But I keep getting the login and signup.
It seems like the session variables are not being "transported".
Any kind of help is appreciated.
PS: Sorry for bad English :P
Thanks

Answer 1

As far as I know anything other then numbers must be enclosed in a ' ' . Just try this one
$checklogin = "SELECT * FROM users WHERE username ='".$_SESSION['username']."' AND password ='".$_SESSION['password']."'";
I hope this works.

Answer 2

To use $_SESSION variables, run session_start() first. The example that you have marked as "in the header of the web site," you're not running session_start() first.
http://php.net/manual/en/function.session-start.php
session_start() creates a session or resumes the current one based on a session identifier passed via a GET or POST request, or passed via a cookie.