Simple Login logout system using php Mysql

Login and logout system is the most important thing for the user management, session management is one important thing for manage the user for the whole time of login time. for that we have to use session for this. it should have 5 files for this. we have to fetch the same value for the user and check the session and register the session value. and make destroy for logout. let see it detail,

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it should need 5 files for this login-logout system, they are

1. login/index page
2. datafetch/usercheck page
3. session/check page
4. welcome/profile page
5. logout page

the above files must me needed for this. we can named it as our wish. let see what i done here. and the database file is needed, if you have any doubt about insert coding check here for insert code 

database name --> 2mylogin
table name --> login

DB.PHP

<?php 
$conn=mysql_connect('localhost','root','');
$db=mysql_select_db('2my4edge',$conn);
?>

INDEX.PHP

<?php
session_start();
?>
<form method="post" name="login" action="login.php">
<label for="name" class="labelname"> Username </label>
<input type="text" name="username" id="userid" required="required" /><br />
<label for="name" class="labelname"> Password </label>
<input type="password" name="password" id="passid" required="required"  /><br />
<input type="submit" name="submit" id="submit"  value="Login" />
</form>

in the index page we have to start the session, as the above mentioned. action is performed in login.php page.

LOGIN.PHP

<?php 
include('db.php');
session_start();
{
    $user=mysql_real_escape_string($_POST['username']);
    $pass=mysql_real_escape_string($_POST['password']);
    $fetch=mysql_query("SELECT id FROM `login` WHERE 

                         username='$user' and password='$pass'");
    $count=mysql_num_rows($fetch);
    if($count!="")
    {
    session_register("sessionusername");
    $_SESSION['login_username']=$user;
    header("Location:profile.php"); 
    }
    else
    {
       header('Location:index.php');
    }

}
?>

if the session is registered then go to check the profile.php page there session.php file is included so the session is checked.

SESSION.PHP

<?php
include('db.php');
session_start();
$check=$_SESSION['login_username'];
$session=mysql_query("SELECT username FROM `login` WHERE username='$check' ");
$row=mysql_fetch_array($session);
$login_session=$row['username'];
if(!isset($login_session))
{
header("Location:index.php");
}
?>

check the session value is correct or not. if the session is value is not set, then again redirect to index.php page.

PROFILE.PHP

<?php
include("session.php");
?>

<h3 align="center"> Hellow <?php echo $login_session; ?></h3> 
<h2 align="center" >Welcome to login system</h2> 

<h4 align="center">  click here to <a href="logout.php">LogOut</a> </h4>

assign the logout.php page in the profile.php page.

LOGOUT.PHP

<?php
session_start();
if(session_destroy())
{
header("Location: index.php");
}
?>

in the logout.php page, we should unset or destroy the session value as the above you seen. then locate to index.php page.
and we should have to start the session in all the page.