插入多个表sql

Question

表1：

Countries:

country_id
country

表2：

User:

user_id
country_id
first_name
infix
last_name
user_name
password

表3：

train_information:

train_id
country_id
user_id
train_name
etc.

当我创建新用户时，我只需选择国家/地区的号码（手动进入）。

但是当用户登录并添加火车时。信息转到train_information。但是它将country_id和user_id保留为NULL。如何让登录用户自动填写？

编辑：

add_train.php

<?php
    require 'top.php';
?>
    <div id="left">
        left
    </div>


    <div id="center">
        <div id='toevoegen_trein'>
            <form action="add_train_send.php" method="post">
                <table>
                    <tr>
                        <td>Train Name:</td>
                        <td><input type="text" name="train_name" required><br></td>
                    </tr>

                    <tr>
                        <td>Tare Weight:</td>
                        <td><input type="text" name="tare_weight" required><br></td>
                    </tr>
                    <tr>
                        <td>Number of Bogies:</td>
                        <td><input type="text" name="number_of_bogies" required><br></td>
                    </tr>
                    <tr>
                        <td>Number of Axles:</td>
                        <td><input type="text" name="number_of_axles"><br></td>
                    </tr>
                    <tr>
                        <td>Wheel Diameter Minimal:</td>
                        <td><input type="text" name="wheel_diameter_min"><br></td>
                    </tr>
                    <tr>
                        <td>Wheel Diameter Maximal:</td>
                        <td><input type="text" name="wheel_diameter_max"><br></td>
                    </tr>
                    <tr>
                        <td><input type="submit" name="toevoegen" value="Next"></td>
                    </tr>
                </table>
            </form>
        </div>
    </div>

    <div id="right">
        right
    </div>
<?php
    require 'bottom.php';
?>

add_train_send.php

<!--This is the header of the site-->
<?php
    require 'top.php';
?>

<!--This is the left side of the page-->
<div id="left">
    left
</div>

<!--This is the center of the page (Where the most content is)-->
<div id="center">
<?php
    //Train is send here//
    $add_train = $database->train_add();
?>
    Train: <?php echo $_POST['train_name']; ?>
    <!--Here we make the number of fields based on the number of axles-->
    <div id="axle_bogie_border">
    <!--The image of the train-->
        <img src="Images/axle_train.png" alt="train">
    <!--The show axles are the number of checkboxes (Filled in by a user)-->
        <div id="show_axles">
            <?php  
                $_POST['number_of_axles'];
                    if(isset($_POST['number_of_axles'])){
                    for($i=0; $i<$_POST['number_of_axles']; $i++){
                        echo "<div id='axle_figure'>" . $i . "</div>";
                    }   
                }
            ?>
        </div>
        <br /> <br />
        <div id="show_bogies">
            <?php  
                $_POST['number_of_bogies'];
                    if(isset($_POST['number_of_bogies'])){
                    for($i=0; $i<$_POST['number_of_bogies']; $i++){
                        echo "<input type='checkbox' name='bogies[$i]'>";
                    }   
                }
            ?>
        </div>
    </div>
</div>

<!--This is the right side of the page-->
<div id="right">
    right
</div>

<!--This is the footer of the website-->
<?php
    require 'bottom.php';
?>

功能：

function train_add() {
            $sql = "INSERT INTO train_information "
        . "(train_name, tare_weight, number_of_bogies, number_of_axles, wheel_diameter_min, wheel_diameter_max)"
        . "VALUES (:train_name, :tare_weight, :number_of_bogies, :number_of_axles, :wheel_diameter_min, :wheel_diameter_max) ";
            $sth = $this->pdo->prepare($sql);
            $sth->bindParam(':train_name', $_POST['train_name'], PDO::PARAM_STR);
            $sth->bindParam(':tare_weight', $_POST['tare_weight'], PDO::PARAM_STR);
            $sth->bindParam(':number_of_bogies', $_POST['number_of_bogies'], PDO::PARAM_STR);
            $sth->bindParam(':number_of_axles', $_POST['number_of_axles'], PDO::PARAM_STR);
            $sth->bindParam(':wheel_diameter_min', $_POST['wheel_diameter_min'], PDO::PARAM_STR);
            $sth->bindParam(':wheel_diameter_max', $_POST['wheel_diameter_max'], PDO::PARAM_STR);
            $sth->execute();    
        }