如果输入类型在PHP中的两个不同文件中，如何插入数据？

Question

基本上我有三个动态下拉列表和4个普通字段，总共有7个。我是通过使用ajax和javascript来完成的。

第一个显示类别

第二个显示我在第一个下拉列表中选择的类别下的子类别

第三个显示我在第二个下拉列表中选择的子类别下的主题。

然后是正常的输入类型，如性别，职业和工作状态。

此文件名为testdropdown.php

<?php
    $con = mysqli_connect("localhost","root","","imetrics");



    ?>


    <form name="form1" action="" method="POST">

        <table>

            <tr>

                <td>Select Category</td>
                <td>

                        <select id="categorydd" name="catdd" onChange="change_category()">

                            <option>--None Selected--</option>

                            <?php
                            $query=mysqli_query($con, "SELECT category_id, categoryname FROM category WHERE ParentCategoryID IS NULL");
                            while($row=mysqli_fetch_array($query)) {
                                ?>
                                <option value="<?php echo $row["category_id"]; ?>"><?php echo $row["categoryname"]; ?></option>

                                <?php
                            }
                            ?>

                        </select>
                </td>

            </tr>

            <tr>

                <td>Select Subcategory</td>

                    <td>

                        <div id="subcategory">

                            <select>

                                <option>-- None Selected--</option>

                            </select>

                        </div>

                    </td>

            </tr>

            <tr>

                <td>Select Topic</td>

                <td>

                    <div id="topic">

                        <select>

                            <option>-- None Selected--</option>

                        </select>

                    </div>

                </td>

            </tr>

            <tr>

                <td>Gender</td>

                <td><input type="radio" name="age" value="male">Male

                    <input type="radio" name="age" value="female">Female

                    <input type="radio" name="age" value="transgender">Transgender

                </td>


            </tr>

            <tr>

           <td>Age Gap Allowed:</td>
                <td><select name="surveyAgeGroup">
                        <option value="">--None Selected--</option>
                <option value="0 18">Below 18</option>
                <option value="18 25">18-25</option>
                <option value="26 35">26-35</option>
                <option value="36 45">36-45</option>
                <option value="46 50">46-50</option>
                <option value="51 100">Above 50</option>
                </select></td>

            </tr>

            <tr>


                <td>Occupation:</td>

                <td><select name="selectOccupation">
                        <option value="">--None Selected--</option>
                        <option value="1">Grade School</option>
                        <option value="2">K-12</option>
                        <option value="3">College</option>
                        <option value="4">Working Student</option>
                        <option value="5">Employed</option>
                        <option value="6">Unemployed</option>
                    </select></td>


            </tr>


                <tr>

                        <td>Work Status</td>

                        <td><select name="employed">
                                <option value="">--None Selected--</option>
                                <option value="1">Part-time</option>
                                <option value="2">Full-time</option>
                                <option value="3">Casual</option>
                            </select></td>

                </tr>

            <tr>

                    <td><input id="btnSaveSurvey" type="submit" name="submit" value="Save Survey">
                    <input id="btnSaveSurvey" type="submit" name="resetsurvey" value="Reset Survey"></td>

                </tr>

            </tr>

        </table>

    </form>

    <script type="text/javascript">

        function change_category()
        {
            var xmlhttp=new XMLHttpRequest();
            xmlhttp.open("GET","ajax.php?category="+document.getElementById("categorydd").value,false);
            xmlhttp.send(null);
            document.getElementById("subcategory").innerHTML=xmlhttp.responseText;


            if(document.getElementById("categorydd").value=="--None Selected--")
            {
            document.getElementById("topic").innerHTML="<select><option>--None Selected--</option></select>";
            }
        }

        function change_subcategory()
        {
            var xmlhttp=new XMLHttpRequest();
            xmlhttp.open("GET","ajax.php?subcategory="+document.getElementById("subcategorydd").value,false);
            xmlhttp.send(null);
            document.getElementById("topic").innerHTML=xmlhttp.responseText;
        }

    </script>

这是第二个名为ajax.php的php文件

<?php
$con = mysqli_connect("localhost","root","","imetrics");

$category= isset($_GET["category"])?$_GET["category"]:"" ; $subcat=isset($_GET["subcategory"])?$_GET["subcategory"]:"";

if($category!=""){

    $query=mysqli_query($con, "SELECT category_id, categoryname FROM category WHERE ParentCategoryID =$category ");
echo "<select id='subcategorydd' onChange='change_subcategory()'>";
    echo " <option>--None Selected--</option>";
while($row=mysqli_fetch_array($query))
{
    echo "<option value='$row[category_id]' selected>"; echo $row["categoryname"]; echo "</option>";
}
    echo "</select>";
}

if($subcat!=""){

    $query=mysqli_query($con, "SELECT * FROM topic WHERE SubCat = $subcat ");
    echo "<select>";
    echo " <option>--None Selected--</option>";
    while($row=mysqli_fetch_array($query))
    {
        echo "<option value='$row[topic_id]' selected>"; echo $row["title"]; echo "</option>";
    }
    echo "</select>";
}

?>

在这种情况下，我将如何以及在何处进行插入查询？我有7个领域。