ต้องการเลือกช่วงเวลาจาก Date time picker ให้ แสดงค่า sum จากคอลัม ครับ

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<link rel="stylesheet" media="all" type="text/css" href="jquery-ui.css" />
<link rel="stylesheet" media="all" type="text/css" href="jquery-ui-timepicker-addon.css" />

<script type="text/javascript" src="jquery-1.10.2.min.js"></script>
<script type="text/javascript" src="jquery-ui.min.js"></script>

<script type="text/javascript" src="jquery-ui-timepicker-addon.js"></script>
<script type="text/javascript" src="jquery-ui-sliderAccess.js"></script>

<script type="text/javascript">
$(function(){

	var startDateTextBox = $('#dateStart');
	var endDateTextBox = $('#dateEnd');

	startDateTextBox.datetimepicker({
	dateFormat: 'yy-mm-dd',
	timeFormat: "HH:mm",
		onClose: function(dateText, inst) {
			if (endDateTextBox.val() != '') {
				var testStartDate = startDateTextBox.datetimepicker('getDate');
				var testEndDate = endDateTextBox.datetimepicker('getDate');
				if (testStartDate > testEndDate)
					endDateTextBox.datetimepicker('setDate', testStartDate);
			}
			else {
				endDateTextBox.val(dateText);
			}
		},
		onSelect: function (selectedDateTime){
			endDateTextBox.datetimepicker('option', 'minDate', startDateTextBox.datetimepicker('getDate') );
		}
	});
	endDateTextBox.datetimepicker({
	dateFormat: 'yy-mm-dd',
		timeFormat: "HH:mm",
		onClose: function(dateText, inst) {
			if (startDateTextBox.val() != '') {
				var testStartDate = startDateTextBox.datetimepicker('getDate');
				var testEndDate = endDateTextBox.datetimepicker('getDate');
				if (testStartDate > testEndDate)
					startDateTextBox.datetimepicker('setDate', testEndDate);
			}
			else {
				startDateTextBox.val(dateText);
			}
		},
		onSelect: function (selectedDateTime){
			startDateTextBox.datetimepicker('option', 'maxDate', endDateTextBox.datetimepicker('getDate') );
		}
	});

});
</script>
<form name="frmdate" id="frmdate" action="whshow.php" enctype="multipart/form-data" method="post">
Start Date : <input type="text" name="dateStart" id="dateStart" value="" />
End Date : <input type="text" name="dateEnd" id="dateEnd" value="" />
<input type="submit" name="btnsubmit" id="btnsubmit" value="Submit" />
</form>

<?php

mysql_connect("localhost","root","sensor") or die(mysql_error());
mysql_select_db("sensorroom") or die(mysql_error());


if(!empty($_POST['dateStart'])){
$result = mysql_query("SELECT SUM(mwh) AS wh_sum FROM power where TIME BETWEEN '".$_POST['dateStart']."' and '".$_POST['dateEnd']."' ORDER BY `time`");}
else{
	$result = mysql_query("SELECT SUM(mwh) AS wh_sum FROM power where TIME ORDER BY `time` ");
}

$row = mysql_fetch_assoc($result);

$sum = $row['wh_sum'];

//echo mysql_result($result, 0);

?>