Ajax发布数据，同时循环PHP

Sorry, I am a beginner. I have some problem about ajax post data from while loop PHP. Here is my code.

Assume that after while loop I have 5 records 5 buttons with different post data each record, but ajax will send only first data of record no matter I click which button in these 5 records ajax will send the same data of first record data

But, if I use $(this).val() ajax will send right data in each records.

Pls help. thx so much.

In PHP.

<?php while($rs = mysql_fetch_array($qr)) { ?>
        <td width="150">
             <input type="text" name="studentid" class="studentid" value="<?=$rs['studentid']?>"/>
      </td>
    <td width="100">
        <select name="ssize" class="ssize">
            <option value="">ไซต์</option>
            <option <?php if($rs['ssize'] == 'S') { ?> selected="selected" <?php } ?> value="S">S</option>
            <option <?php if($rs['ssize'] == 'M') { ?> selected="selected" <?php } ?> value="M">M</option>
        </select>
    </td>
    <button value="<?=$rs['id']?>" class="printBill btn btn-primary">
            <i class="glyphicon glyphicon-duplicate"> </i>
            พิมพ์ใบเสร็จ
    </button>
<?php } ?>

In JS.

$(".printBill").click(function () {
            $.ajax({
            url: "admin_search_save.php",
            data: {
                id:$(this).val(),
                studentid:$(".studentid").val(),
                ssize:$(".ssize").val(),
            },
            success: function (data) {
            }
        });
    });

You need to use event delegation for dynamically added content.

$(document).on('click','.printBill',function () {

        // capture input and select value by traversing up into parent(tr),
        // then find element [input, select]
        // this traversing method depend on your table structure
        var studID    = $(this).closest('tr').find('input[name=studentid]').val(),
            ssizeData = $(this).closest('tr').find('select[name=ssize]').val();

        $.ajax({
        url: "admin_search_save.php",
        data: {
            id        : $(this).val(),
            studentid : studID,
            ssize     : ssizeData,
        },
        success: function (data) {
        }
    });
  });