多条件查询

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
</head>

<body>
<h1>汽车表</h1>
<?php
include("../DBDA.php");
$db=new DBDA();
//查询时查询框里面显示用
$value1="";
$value2="";
//select语句条件用   条件必须是恒等的
$cx="";
$tj1=" 1=1";
$tj2=" 1=1";

if(!empty($_POST["name"]))
{
	$tj1=" name like '%{$_POST['name']}%'";
	$value1=$_POST["name"];
}

if(!empty($_POST["brand"]))
{
	$tj2=" brand='{$_POST['brand']}'";
	$value2=$_POST["brand"];
}

$cx=" where {$tj1} and {$tj2}";
?>
<form action="dtjchaxun.php" method="post">
<div>
  请输入名称：<input type="text" name="name" value="<?php  echo $value1 ?>"/>
  请输入系列：<input type="text" name="brand" value="<?php echo $value2 ?>"/>
  <input type="submit" value="查询" />
</div>
</form>

<table border="1" width="100%" cellpadding="0" cellspacing="0">
  <tr>
    <td>代号</td>
    <td>名称</td>
    <td>系列</td>
    <td>时间</td>
    <td>油耗</td>
    <td>价格</td>
  </tr>
  <?php
   $sql="select * from car".$cx;
   $zhi=$db->Query($sql);
   
   foreach($zhi as $v)
   {
	   $daiti1="<mark>{$value1}</mark>";
	   $daiti2="<mark>{$value2}</mark>";
	   
	   $th1=str_replace($value1,$daiti1,$v[1]);
	   $th2=str_replace($value2,$daiti2,$v[2]);
	   
	   echo"<tr>
	          <td>{$v[0]}</td>
			  <td>{$th1}</td>
			  <td>{$th2}</td>
			  <td>{$v[3]}</td>
			  <td>{$v[4]}</td>
			  <td>{$v[7]}</td>
	        </tr>";
   }
  ?>
</table>
</body>
</html>
　　页面不查询的时候显示
查询时页面显示