$SESION İLE id çekme

<?php
include ("uerp_baglan.php");
ob_start();
session_start();
    if($_POST)
    {
        $username = stripslashes($_POST["username"]);
        $password = stripslashes($_POST["password"]);


        $query = $conn->query("SELECT * FROM kullanicilar WHERE username='$username' AND password='$password'",PDO::FETCH_ASSOC);
        if ( $say = $query -> rowCount() ){
            if( $say > 0 ){
                echo'yanlş0';
            }else{
        $_SESSION["login"] = "true";
        $_SESSION["username"] = $username;
        $_SESSION["password"] = $password;

                 echo '<div class="alert alert-success">
                    <strong>Başarılı! </strong> Giriş Başarılı </div>';
                    header('Location:index.php');
            }
        }else{
             echo '<div class="alert alert-danger">
                    <strong>Hata! </strong> Kullanıcı Adı Veya Şifre Hatalı</div>';
        }
    }
?>

<?phpinclude ("uerp_baglan.php");ob_start();session_start();    if($_POST)    {        $username = stripslashes($_POST["username"]);        $password = stripslashes($_POST["password"]);        $query = $conn->query("SELECT * FROM kullanicilar WHERE username='$username' AND password='$password'",PDO::FETCH_ASSOC);        if ( $say = $query -> rowCount() ){            if( $say > 0 ){                echo'yanlş0';            }else{        $_SESSION["login"] = "true";        $_SESSION["username"] = $username;        $_SESSION["password"] = $password;        $_SESSION["user_id"] = $query['dbdekiuseridniz'];                 echo '<div class="alert alert-success">                    <strong>Başarılı! </strong> Giriş Başarılı </div>';                    header('Location:index.php');            }        }else{             echo '<div class="alert alert-danger">                    <strong>Hata! </strong> Kullanıcı Adı Veya Şifre Hatalı</div>';        }    }?>