使用下拉列表填充字段

I have a Dropdown list that is populated by MySQL database using the following code

<?php

                    $conn = new mysqli('localhost', 'root', '@', '')
                    or die ('Cannot connect to db');

                    $result = $conn->query("select name, surname FROM clients");
                    echo "<html>";
                    echo "<body>";
                    echo "<select name='client_name' id='client'>";

                    while ($row = $result->fetch_assoc()) {

                        unset($msisdn, $contract_type, $provider);
                        $name = $row['name'];
                        $surname = $row['surname'];
                        echo '<option value="'.$name.'_'.$surname.'">'.$name.' '.$surname.'</option>';
                    }
                    echo "</select>";
                    echo "</body>";
                    echo "</html>";
                    ?>

I want to populate different fields with information related to the result in the drop down list.

<input type="text" name="address">
<input type="text" name="tel">
<input type="text" name="id_nr">

$('#client').change(function() {
    selectedOption = $('option:selected', this);
    $('input[name=address]').val( selectedOption.data('address') );
    $('input[name=tel]').val( selectedOption.data('tel') );
    $('input[name=id_nr]').val( selectedOption.data('id_nr') );
});

You should set data to option as

echo '<option data-address-"'.$address.'" value="'.$name.'_'.$surname.'">'.$name.' '.$surname.'</option>';

Also, update your query to get address along with name & surname.