combobox.php

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <script type='text/javascript' src='http://code.jquery.com/jquery-2.1.3.js'></script>
    <script>
        //<![CDATA[
        $(window).load(function(){
        $("#harga").on("change", function(){
            var nilai = $("#harga :selected").attr("data-harga");
            $("#hasil").val(nilai);
        });
        });//]]>
    </script>
</head>
<body>

    <select id="harga">
        <option value="">Pilih</option>
        <?php
        include "config.php";
        $pos=mysql_query("SELECT * from t_pelanggan order by no_pelanggan");
        while ($r_pos=mysql_fetch_array($pos)) {
        ?>
        <option value="<?php echo $r_pos['no_pelanggan'] ?>" data-harga="<?php echo $r_pos['nama'] ?>"><?php echo $r_pos['no_pelanggan'] ?></option>
        <?php
        }
        ?>
    </select>


    <br>
    <input type="text" id="hasil">
</body>
</html>