Not sure if using isset correctly - php

Question

I am building up a website that must not show login option when the user is already logged in, i.e. session is active. I have tried working with this but its not returning the desired output. Please help. Thanks.
<?php
if(!isset($_SESSION)) {echo "<li><a href='Employee.php'>Login</a></li>";}
?>
edit:
I am adding the part where I check login details from database and start session.
$query = "SELECT Cust_FName from customer where Cust_ID='$name' and Password='$pass'";
$result = mysqli_query($con, $query);
if(mysqli_num_rows($result)!= false)
{
$row = mysqli_fetch_row($result);
echo row[0];
if(mysqli_num_rows($result) > 0)
{
echo "Logged in!";
session_start();
$_SESSION['userName'] = $row[0];
header("Location: index.php");
}
}

Answer 1

If you want to check if the session is started, you can use
if(session_status() != PHP_SESSION_ACTIVE) {
echo "<li><a href='Employee.php'>Login</a></li>";
}
The problem is that the session als also there if the user isn't logged in. You have to check if e.g. $_SESSION['user_id'] is set:
if(!isset($_SESSION['user_id']) {
echo "<li><a href='Employee.php'>Login</a></li>";
}
In my example $_SESSION['user_id'] will be filled when the user login was successful.

Answer 2

Problem
From your comment:
The login button should only show up when the user has not logged in, and once he does, it should disappear.
Solution
// This would be your login.php page
<?php
session_start();
// process your HTML form, like this
if(isset($_POST['login'])){
// Remember: always validate your form inputs
$name = $_POST['name'];
$pass = $_POST['pass'];
$query = "SELECT Cust_FName from customer where Cust_ID='$name' and Password='$pass'";
$result = mysqli_query($con, $query);
if(mysqli_num_rows($result)!= false){
$row = mysqli_fetch_row($result);
//echo row[0];
if(mysqli_num_rows($result) > 0){
//echo "Logged in!";
$_SESSION['userName'] = $row[0];
header("Location: index.php");
exit(); // exit() is necessary, otherwise the script execution is not terminated. Setting header alone is not enough to redirect.
}
}
}
if(isset($_SESSION['userName'])){
// user is already logged in
// redirect the user to a different page
// header("Location: index.php");
// exit();
}else{
// user is not logged in
// display login option
?>
<!--Your HTML form for login-->
<form action="login.php" method="POST">
<input type="text" name="name" value="" /><br />
<input type="text" name="pass" value="" /><br />
<input type="submit" name="login" value="Login" />
</form>
<?php
}
?>
Edited:
Session is a file that resides in our server and in that file we can store any amount of information. We generally deploy a session cookie on the client's browser.
Before we output any HTML or white space, we need to start our session.
When we do like this,
<?php
session_start();
?>
It will say, go to the browser, get the session id and open the appropriate file and if it didn't find any session id, it will start a new session. User can only see session id, nothing else.
Tip: Remember to clean up sessions from time to time.

Answer 3

Put in the login page
<?php
session_start();
// Store Session Data
$_SESSION['login_user']= $username; // Initializing Session
?>
when you have to check use
<?php
session_start();
// Store Session Data
if(isset($_SESSION['login_user'])){
//do things
}
?>
and on logout
<?php
session_destroy();
?>