ajax.html:
<!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=gb2312" />
<title>Ajax教程</title>
<script language="javascript" type="text/javascript">
//浏览器支持代码
function ajaxFunction(){
    var ajaxRequest;        //xmlHttpRequest对象
        
    try{
        // Opera 8.0+, Firefox, Safari
        ajaxRequest = new XMLHttpRequest();
    } catch (e){
        // IE系列
        try{
            ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
        } catch (e) {
            try{
                ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (e){
                // 古老的浏览器
                alert("你的浏览器不支持Ajax!");
                return false;
            }
        }
    }
        
    // 创建一个函数负责介绍来自服务器的数据
    ajaxRequest.onreadystatechange = function(){
        if(ajaxRequest.readyState == 4){
            var ajaxDisplay = document.getElementById('ajaxDiv');
            ajaxDisplay.innerHTML = ajaxRequest.responseText;
        }
    }

    var age = document.getElementById('age').value;
    var wpm = document.getElementById('wpm').value;
    var sex = document.getElementById('sex').value;
    var queryString = "?age=" + age + "&wpm=" + wpm + "&sex=" + sex;
    ajaxRequest.open("GET", "ajaxmysql.php" + queryString, true);        
    ajaxRequest.send(null);        
}
</script>
</head>
<body>
<form name='myForm'>
最大年龄: <input type='text' id='age' /> <br />
最大打字速度WPM(words per minute): <input type='text' id='wpm' />
<br />
性别: <select id='sex'>
<option value='m'>男</option>
<option value='f'>女</option>
</select>
<input type='button' onclick='ajaxFunction()' value='查询mysql' />
</form>
<div id='ajaxDiv'>这里显示结果.</div>
</body>
</html>
前台的字符集编码是国标gb2312保存的按gb2312编码保存(用的emeditor编辑器).
 
后台页面ajaxmysql.php:
<?php
header("Content-Type:text/html;charset=utf-8");//页面的字符集编码
$dbhost = "localhost";
$dbuser = "root";
$dbpass = "123456";
$dbname = "ajax";
//连接mysql
mysql_connect($dbhost, $dbuser, $dbpass);
//选择数据库
mysql_select_db($dbname) or die(mysql_error());

mysql_query("set names utf8");//防止查询乱码

//检索 查询串
$age = $_GET['age'];
$sex = $_GET['sex'];
$wpm = $_GET['wpm'];

// 防止注入
$age = mysql_real_escape_string($age);
$sex = mysql_real_escape_string($sex);
$wpm = mysql_real_escape_string($wpm);

//构造查询
$query = "SELECT * FROM ex1 WHERE sex = '$sex'";
if(is_numeric($age))
$query .= " AND age <= $age";
if(is_numeric($wpm))
$query .= " AND wpm <= $wpm";

//执行查询
$qry_result = mysql_query($query) or die(mysql_error());

//结果串
$display_string = "<table>";
$display_string .= "<tr>";
$display_string .= "<th>姓名</th>";
$display_string .= "<th>年龄</th>";
$display_string .= "<th>性别</th>";
$display_string .= "<th>打字速度</th>";
$display_string .= "</tr>";

// 为每一个返回的人插入一行.
while($row = mysql_fetch_array($qry_result)){
    $display_string .= "<tr>";
    $display_string .= "<td>{$row['name']}</td>";
    $display_string .= "<td>{$row['age']}</td>";
    $display_string .= "<td>{$row['sex']}</td>";
    $display_string .= "<td>{$row['wpm']}</td>";
    $display_string .= "</tr>";
}
echo "查询: " . $query . "<br />";
$display_string .= "</table>";
echo $display_string;
?>

后台页面编码utf-8.

主要考虑ajax的utf8做的改动。