SELECT Parent category from drop down, it will show child category in another drop down but repeating same child category

Question

I'm facing an issue that I have created 2 tables one is parent_category and another is child_category. I fetch the parent categories in select option drop down. My aim is to fetch the child category from child table with parent id that is same in both table. I have tried many time but when I select parent category it will show me the same name categories many time in child select option drop down.

Here is my code.

index.php

<div>
        <select id="parent_category">
            <?php 
                $select = "select * from categories";
                $run = mysqli_query($con, $select);
                while($row = mysqli_fetch_array($run)){
                    echo "<option value='".$row['id']."'>".$row['name']."</option>";
                }
            ?>
        </select>

        <br><br>

        <select id="child_category">

        </select>
    </div>

    <script src="https://code.jquery.com/jquery-3.6.0.min.js"
        integrity="sha256-/xUj+3OJU5yExlq6GSYGSHk7tPXikynS7ogEvDej/m4=" crossorigin="anonymous"></script>
    <script>
    $(document).ready(function() {
        $('#parent_category').on('change', function() {
            let id = $(this).find(':selected').data('id');
            alert(id);
            $.ajax({
                url: 'data.php',
                method: 'GET',
                data: {
                    id: id,
                },
                success: function(data) {
                    $("#child_category").html(data);
                }
            });
        });
    });
    </script>

data.php

    $con = mysqli_connect("localhost", "root", "", "nilam-ghar");

    if(isset($_GET["id"])){
        $output = "";
        $id = $_GET['id'];
        $get = "SELECT * FROM child_category WHERE parent_cat_id='$id'";
        $run = mysqli_query($con, $get);
        while($row = mysqli_fetch_array($run)){
            echo $output .= '
                <option>'.$row["name"].'</option>;
            ';
        }

        echo $output;
    }

database tables

parent_category:
id(int)     date(date)    name(text)

child_category:
id()int     date(date)    parent_cat_id(int)    name(text)

**Note:** data exits in both table. in child category, parent id also exist.

Answer 1

just checked your code found issue here let id = $(this).find(':selected').**data('id');** data('id') this will use when you assign <option data-id="1">OptionA</option> like this in your case your case you have used value attribute of option so

let id = $(this).find(':selected').val();

you will get value like this.

Also you can checkout below snippet, having more clear vision.

 $(document).ready(function() { $('#parent_category').on('change', function() { let id = $(this).find(':selected').val(); let option = $(this).find(':selected').text(); console.log('ID => '+id+' Option => '+option); }) })

 <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> <select id="parent_category"> <option value="">Select</option> <option value="1">OptionA</option> <option value="2">OptionB</option> <option value="3">OptionC</option> </select>

Answer 2

Two things seems to be wrong in your code.

First, in your JavaScript you're getting the data-id attribute to make the query, but your <option> s don't have this attribute. So, try changing

let id = $(this).find(':selected').data('id');

for

let id = $(this).find(':selected').val();

Also, in your data.php , it seems that you're echoing the output twice, so try the following:

    // (...)

    while($row = mysqli_fetch_array($run)){
        // removed 'echo' in the line below
        $output .= '
            <option>'.$row["name"].'</option>;
        ';
    }

    // (...)