php+ajax注册验证实例(完整代码)

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;
}

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 = "<font color=red>已经被注册！</font>";
  }else
  {
   $response = "<font color=blue>恭喜！可以注册！</font>";
  }
  
  echo $response;
}

?>

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;