Okay i have looked through most of the web for the past 2 days, and i can't find anything that brings me closer to a solution. So now i'm asking you guys.
I am creating a ''Library'' system with login, reservations and what not.
I am stuck on the part where i have to attach data on an item to a unique user ID. The idea i had was to take data from table 1, add in 2 input fields and the $_Session[''] and store it together as one row in a seperate table. This is the code i've got so far:
(Sensitive information is changed to something with bunny.)
<?
$MA = $_SESSION['MA_NR'];
$Bunny_Nr = $_POST['Skriv_Bunny'];
$Ordre_Nr = $_POST['Skriv_VO'];
$Ordre_Nr_sub = $_POST['Submit_VO'];
if(isset($Ordre_Nr_sub));
{
    $Bunny ="SELECT Bunny_No, 
                        Serie_No, 
                            Model, 
                                Kal_Frekvens, 
                                    Sidste_Kal,
                                        Næste_Kal 
                                            FROM Cluster
                                                WHERE Bunny_No = '$bunny_Nr'";
    $Result2= mysqli_query($conn, $Bunny);
    $Row2 = mysqli_fetch_assoc($Result2);
    $SQLinto ="INSERT INTO Udlaan (Bunny_No, 
                                        Serie_No, 
                                            Model, 
                                                Kal_Frekvens, 
                                                    Sidste_Kal, 
                                                        Næste_Kal, 
                                                            Laaner, 
                                                                Ordre_No) 
                                VALUES(" . $Row2['0'] .", 
                                            ".$Row2['1'].", 
                                                ".$Row2['2'].", 
                                                    ".$Row2['3'].", 
                                                        ".$Row2['4'].", 
                                                            ".$Row2['5'].", 
                                                                ".$MA.", 
                                                                    ".$Ordre_Nr.")";}
    $Result_into = mysqli_query($conn, $SQLinto);
?>
