php+ajax注册验证实例(完整代码)

var xmlHttp
function showHint(str)
{
if (str.length==0)
{
document.getElementById("txtHint").innerHTML=""
return
}
xmlHttp=GetXmlHttpObject()
if (xmlHttp==null)
{
alert ("Browser does not support HTTP Request")
return
}
xmlHttp.onreadystatechange=stateChanged

var geturl="conn.php?q="+str
//sid是增加一个随机数 防止页面启用缓存技术·
geturl=geturl+"&sid="+Math.random()
geturl=encodeURI(geturl);
geturl=encodeURI(geturl);
xmlHttp.open("GET",geturl,true)
xmlHttp.send(null)
}
function stateChanged()
{
if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
{
document.getElementById("txtHint").innerHTML=xmlHttp.responseText
}
}
function GetXmlHttpObject()
{
var xmlHttp=null;
try
{
// Firefox, Opera 8.0+, Safari
xmlHttp=new XMLHttpRequest();
}
catch (e)
{
// Internet Explorer
try
{
xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
}
catch (e)
{
xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
}
}
return xmlHttp;
}

$q=$_GET["q"];
$q = urldecode($q);

if (strlen($q) > 0)
{
$conn = @mysql_connect("localhost","root","1010") or die ("MySql连接错误");
mysql_select_db("xin",$conn);
mysql_query("set names 'utf8'");

$sql = "SELECT username FROM message WHERE username = '$q'";
$query = mysql_query($sql);
@$row = mysql_fetch_array($query);

if(!empty($row['username']))
{
$response = "已经被注册！";
}else
{
$response = "恭喜！可以注册！";
}

echo $response;
}

?>

DROP DATABASE IF EXISTS `xin`;
CREATE DATABASE `xin` /*!40100 DEFAULT CHARACTER SET utf8 */;
USE `xin`;

CREATE TABLE `message` (
`id` int(11) NOT NULL auto_increment,
`username` varchar(20) default NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;