Log in log out session php

Question

I have here the code of my login and logout can you guys check if the session I placed is correct?

Login code :

<?php
session_start();

header("Cache-Control: no-store, no-cache, must-revalidate, max-age=0");
header("Cache-Control: post-check=0, pre-check=0", false);
header("Pragma: no-cache");
header('Content-Type: text/html');

$connection = mysql_connect("localhost", "root", "");
$db = mysql_select_db("store_data", $connection);

if(isset($_POST['login'])){
    $admin=$_POST['user'];
    $pass=$_POST['pass'];
    $select_user = mysql_query("SELECT admin_name FROM admin");
    $select_pass = mysql_query("SELECT admin_pass FROM admin");
    $result_1 = mysql_fetch_assoc($select_user);
    $result_2 = mysql_fetch_assoc($select_pass);

    if($admin !=$result_1['admin_name'] || $pass!=$result_2['admin_pass']){
        echo "<script >alert('Invalid password or username')</script>";
        header("refresh:0; url=administrator.php" );
    }

Logout code :

<?php

session_destroy();
header("Location: administrator.php");

?>

Answer 1

Before session_destroy you need session_start

<?php    
session_start();
session_destroy();
header("Location: administrator.php");
?>

Answer 2

Errors

1. session_start() missing in logout
2. You not check $admin and $pass value in your query
3. Your Argument is wrong in the set session
4. And you not setting any session to destroy it
5. Don't use MySQL Function Its depreciated now

In logout

<?php
    session_start(); //add this
    session_destroy();
    header("Location: administrator.php");
?>

In login

<?php

    session_start();

    header("Cache-Control: no-store, no-cache, must-revalidate, max-age=0");
    header("Cache-Control: post-check=0, pre-check=0", false);
    header("Pragma: no-cache");
    header('Content-Type: text/html');

    $connection = mysql_connect("localhost", "root", "");
    $db = mysql_select_db("store_data", $connection);

    if(isset($_POST['login']))
    {
        $admin=$_POST['user'];
        $pass=$_POST['pass'];

        $query = mysql_query("SELECT * FROM admin where admin_name='$admin' AND admin_pass = '$pass' ");

        $result = mysql_fetch_assoc($query);
        $count = count($result);

        if(!empty($count))
        {
            $_SESSION["admin_name"] = $admin;
            header("refresh:0; url=administrator.php" );
        }
        else
        {
            echo "Invalid User";
        }
    }