$sql = "INSERT INTO orders (orderID) VALUES ('.$rnd_id.'); ";
        $sql.= "INSERT INTO order_details (
            orderID,
            orderType,
            orderDate,
            orderTime,
            quantity,
            orderPrice,
            discount,
            discountPrice,
            employeeID
            )
            SELECT
            '.$rnd_id.' ,
            '.$type.'   ,
            '.$date.'   ,
            '.$time.'   ,
            '.$quantity.' ,
            (unitPrice * '.$quantity.'),
            '.$dis.'  ,
            (unitPrice * '.$quantity.') - ((unitPrice * '.$quantity.') * '.$dis.') ,
            '.$eid.'
            FROM product WHERE productID = '.$pid.'
            ; ";

        if (!$link->multi_query($sql)) {
            echo "Multi query failed: (" . $link->errno . ") " . $link->error;
        }

        do {
            if ($res = $link->store_result()) {
                var_dump($res->fetch_all(MYSQLI_ASSOC));
                $res->free();
            }
        } while ($link->more_results() && $link->next_result());

product

productID
productName
categoryID
unitPrice
unitsInStock
discontinued

order_details

orderID
orderType
orderDate
orderTime
productID
quantity
orderPrice
discount
discountPrice
employeeID