php+mysql查询问题，新手，不知道到底哪儿出了问题，烦死了

原本想点击Client ID就按client_id排序，点击Order Time就按order_time排序。。。。
可是点击了没有用，不知道是哪儿出现了问题，新手求大家帮忙解决一下哈~

<?php
require_once "D:\PHP\pear\HTML\Table.php";
//连接数据库
$mysqli=new mysqli("localhost","root","xxxxxxxx","lianxi1");
//创建表属性数组
$attributes=array("border"=>"1");
//创建表对象
$table=new HTML_Table($attributes);
//创建表头链接
$orderID="Order ID";
$clientID="Client ID";
$time="Order Time";
$subtotal="Sub Total";
$shipping="Shipping Cost";
$totalcost="Total Cost";
//设置首部
$table->setHeaderContents(0,0,$orderID);
$table->setHeaderContents(0,1,$clientID);
$table->setHeaderContents(0,2,$time);
$table->setHeaderContents(0,3,$subtotal);
$table->setHeaderContents(0,4,$shipping);
$table->setHeaderContents(0,5,$totalcost);
//创建和执行查询
$sort=(isset($_GET['sort'])) ? $_GET['sort'] : "id";

$columns=array('id','client_id','order_time','sub_total','shipping_cost','total_cost');
if(in_array($sort,$columns)){
$query="select id as Order ID,client_id as Client ID,
order_time as Order Time,concat('$',sub_total) as Sub Total,
concat('$',shipping_cost) as Shipping Cost,
concat('$',total_cost) as Total Cost from sales order by ? asc";
$stmt=$mysqli->prepare($query);
//绑定参数
$stmt->bind_param('s',$sort);
$stmt->execute();}
//绑定结果
$stmt->bind_result($id,$client_id,$order_time,$sub_total,$shipping_cost,$total_cost);

//格式化每一行
$rownum=1;
while($stmt->fetch()){
$table->setCellContents($rownum,0,$id);
$table->setCellContents($rownum,1,$client_id);
$table->setCellContents($rownum,2,$order_time);
$table->setCellContents($rownum,3,$sub_total);
$table->setCellContents($rownum,4,$shipping_cost);
$table->setCellContents($rownum,5,$total_cost);
$rownum++;
}
//输出数据
echo $table->toHTML();
//关闭数据库
$mysqli->close();
?>

先看点击以后，你的代码有么有执行，执行到什么位置了，是不是逻辑有问题。