if session redirect to homepage - php

Question

if(!$_SESSION['username']) {
$ip = $db->real_escape_string(VisitorIP());
$username = $db->real_escape_string($_POST['username']);
$password = $db->real_escape_string($_POST['password']);
$salt = "****";
$password = md5($password . $salt);
$result = $db->query("SELECT * FROM TABLE WHERE username='$username' and password='$password'");
$count = mysqli_num_rows($result);
if ($count == 1){
$bannedq = $db->query("SELECT banned FROM TABLE WHERE username='$username' AND password='$password'");
$banned = $bannedq->fetch_row();
if($banned[0] == "1") {
$failedLogin="1";
$message = 'You are banned and you cannot login';
} else {
$ip = $db->real_escape_string(VisitorIP());
$db->query("UPDATE h_users SET lastlogin=now(), lastip = '$ip' WHERE username='$username'");
header("Location: home");
session_start();
$_SESSION['username'] = $username;
$_SESSION['password'] = $password;
$failedLogin = "1";
$message = 'Username or Password WRONG!';
}
}
} else {
header("location: home");
}
Hello programmers,
I am trying to setup a login system in my website. Until now it was working fine but when the session is set and the user gets redirected to the homepage now if he goes to the login screen and the session is set i want him to redirect to the homepage and not see the login screen again.
But my after i added this part :
if(!$_SESSION['username']) {
it does not work

Answer 1

You have to take your session start and put it there before you use it, so write this before your if statement:
session_start();
if(!$_SESSION['username']) {
//...
And delete this one here:
/...
session_start();
$_SESSION['username'] = $username;
$_SESSION['password'] = $password;
/...
(Also i would add a die(); or exit(); after each header, it makes sure nothing gets executed after the header)

Answer 2

Okay guys thanks for your help <3 <3
I changed my code to this and everything went fine
session_start();
if(!isset($_SESSION['username'])) {
if(isset($_POST['username']) && isset($_POST['password'])) {
$ip = $db->real_escape_string(VisitorIP());
$username = $db->real_escape_string($_POST['username']);
$password = $db->real_escape_string($_POST['password']);
$salt = "ho073";
$password = md5($password . $salt);
$result = $db->query("SELECT * FROM TABLE WHERE username='$username' and password='$password'");
$count = mysqli_num_rows($result);
if ($count == 1){
$bannedq = $db->query("SELECT banned FROM TABLE WHERE username='$username' AND password='$password'");
$banned = $bannedq->fetch_row();
if($banned[0] == "1") {
$failedLogin="1";
$message = 'You are banned and you cannot login';
} else {
$ip = $db->real_escape_string(VisitorIP());
$db->query("UPDATE TABLE SET lastlogin=now(), lastip = '$ip' WHERE username='$username'");
header("Location: home");
$_SESSION['username'] = $username;
$failedLogin = "1";
$message = 'Username or Password WRONG!';
}
}
}
include'templates/login.html';
} else {
header("location: home");
die();
}
Much love for you <3