Refresh the page with new request on change select option - php

Question

I am trying to achieve something via php.
Here there are couple of options.
<select class="custom-select" id="inputGroupSelect01">
<option selected="">Select Clusters ...</option>
<option value="math-related">Math Related</option>
<option value="science-related">Science Related</option>
</select>
There are Group of subject fields which will appear when the options are changed respectively.
<div class="form-row pb-5" id="math-related"">
<div class="form-group col-md-3">
<input type="number" class="form-control" id="num1" placeholder="English">
</div>
<div class="form-group col-md-3">
<input type="number" class="form-control" id="num2" placeholder="Math">
</div>
<div class="form-group col-md-3">
<input type="number" class="form-control" id="num3" placeholder="Science">
</div>
<div class="form-group col-md-3">
<input type="number" class="form-control" id="num4" placeholder="Computer">
</div>
</div>
When the option is changed to Math related OR Science Related option, the related 5-6 subject fields will be populated like image below. Some might have 5, some might have 8.
How to refresh the page and load the new sets of input fields according to selection done via PHP?
Example Image for fields

Answer 1

First of all change your select dropdown with your page url + parameter and make sure to replace YOUR_PAGE_URL with actual url as follows -
<select onChange="window.location.href=this.value" class="custom-select" id="inputGroupSelect01">
<option value="">Select Clusters ...</option>
<option value="YOUR_PAGE_URL?topic=math-related">Math Related</option>
<option value="YOUR_PAGE_URL?topic=science-related">Science Related</option>
</select>
After then just do a GET parameter checking on your page to populate your fields like -
if( issset($_GET['topic']) ){
if( $_GET['topic'] == 'math-related' ){
echo "Add your math related above 5-8 fields html here.";
}elseif( $_GET['topic'] == 'science-related' ){
echo "Add your science related above 5-8 fields html here.";
}
}