PHP实现多关键字加亮功能

<?php 
$conn = @ mysql_connect("localhost", "root", "") or die("数据库链接错误"); 
mysql_select_db("form", $conn); 
mysql_query("set names 'gbk'"); 
?> 

<?php 
include 'conn.php'; 
?> 
<table width=500 align="center"> 
  <form action="" method="get"> 
  <tr> 
   <td>关键字：<input type="text" name="keyWord" /> 
   <input type="submit" value="搜索" /></td> 
  </tr> 
  </form> 
 </table> 
 
 <table width=500 border="0" align="center" cellpadding="5" 
  cellspacing="1" bgcolor="#add3ef"> 
  <?php 
  //关键字不为空的时候才执行相关搜索 
  if($_GET['keyWord']){ 
  //用空格符把关键字分割开 
  $key=explode(' ', $_GET[keyWord]); 
  $sql="select * from message where title like '$key[0]' or title like '$key[1]' or content like '$key[0]' or content like '%$key[1]%'"; 
  $query=mysql_query($sql); 
  while ($row=mysql_fetch_array($query)){ 
   //替换关键字，并且把关键字高亮显示 
   $row[title]=preg_replace("/$key[0]/i", "<font color=red><b>$key[0]</b></font>", $row[title]); 
   $row[title]=preg_replace("/$key[0]/i", "<font color=red><b>$key[1]</b></font>", $row[title]); 
   $row[content]=preg_replace("/$key[0]/i", "<font color=red><b>$key[0]</b></font>", $row[content]); 
   $row[content]=preg_replace("/$key[1]/i", "<font color=red><b>$key[1]</b></font>", $row[content]); 
   ?> 
 
  <tr bgcolor="#eff3ff"> 
   <td>标题：<font color="black"><?=$row[title]?></font> 用户：<font color="black"><?=$row[user] ?></font> 
   <div align="right"><a href="preEdit.php?id=<?=$row[id]?>">编辑</a>&nbsp;&nbsp;|&nbsp;&nbsp;<a 
    href="delete.php?id=<?=$row[id]?>">删除</a></div> 
   </td> 
  </tr> 
  <tr bgColor="#ffffff"> 
   <td>内容：<?=$row[content]?></td> 
  </tr> 
  <tr bgColor="#ffffff"> 
   <td> 
   <div align="right">发表日期：<?=$row[lastdate]?></div> 
   </td> 
  </tr> 
  <?php } 
  } 
  ?> 
 </table> 

//用空格符把关键字分割开 
 $key=explode(' ', $_GET[keyWord]);