การเช็ค username ซ้ำ ค่ะ ให้มีข้อความเตือน เวลาที่ เช็คว่าเกิดค่าซ้ำ ค่ะ

		$sql = "select name from tb_name  where name='$_POST[name]'";
		$result=mysql_query($sql);
		$rows =mysql_num_rows($result);
		$i=0;
		if($rows>$i){
?>
	 		 <script>
			 alert("ขออภัย ชื่อนี้มีอยู่ในระบบแล้ว กรุณากลับไปเพิ่มชื่อเข้ามาใหม่");
					window.location="new.php";
			</script>
<?
		}else{ echo "ชื่อนี้ยังไม่มี ผ่านครับ";}

	$strSQL = "SELECT * FROM member WHERE username = '".$username."' ";
	$objQuery = mysql_query($strSQL) or die ("Error Query [".$strSQL."]");
	$objResult = mysql_fetch_array($objQuery);
	if($objResult)
	{
		echo "<img src='../images/false.png'> username ซ้ำค่ะกรอกใหม่นะคะ" ;
	}
	else
	{
		echo "<img src='../images/true.png'>";
	}

<script language="JavaScript">
var HttPRequest = false;
function CallPOSTRequest(url,parameters) {
HttPRequest = false;
if (window.XMLHttpRequest) { // Mozilla, Safari,...
HttPRequest = new XMLHttpRequest();
if (HttPRequest.overrideMimeType) {
HttPRequest.overrideMimeType('text/html');
}
} else if (window.ActiveXObject) { // IE
try {
HttPRequest = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try {
HttPRequest = new ActiveXObject("Microsoft.XMLHTTP");
} catch (e) {}
}
} 

if (!HttPRequest) {
alert('Cannot create XMLHTTP instance');
return false;
}


HttPRequest.onreadystatechange = alertContener;
HttPRequest.open('POST', url, true);
HttPRequest.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
HttPRequest.setRequestHeader("Content-length", parameters.length);
HttPRequest.setRequestHeader("Connection", "close");
HttPRequest.send(parameters);
}

function alertContener() {
if (HttPRequest.readyState == 4) {
if (HttPRequest.status == 200) {
result = HttPRequest.responseText;
document.getElementById('myspan').innerHTML = result; 
} else {
//alert('There was a problem with the request.');
result = HttPRequest.responseText;
document.getElementById('myspan').innerHTML = result; 
}
}
}


function SubmitContent(value) {
document.getElementById('myspan').style.visibility = 'hidden';
document.getElementById('myspan').style.visibility = 'visible';

var poststr = "User=" + encodeURI(document.getElementById('username').value);
CallPOSTRequest('chk_regis.php',poststr);
</script>

<form id="myform" action="" method="post">
<input name="username" type="text" class="textfied" onKeyPress="return bannedKey(event)">
<input name="Check" type="button" class="button_forget" id="Check" OnClick="JavaScript:SubmitContent();" value="Check">
&nbsp;&nbsp;<span id="myspan"></span><br>
</form>
}

 <? 
mysql_connect("localhost","root","1234"); 
mysql_select_db("yourdatabase"); 

$strSQL = "SELECT * FROM member WHERE username = '".trim($_POST["User"])."' "; 
$objQuery = mysql_query($strSQL); 
$intRows = mysql_num_rows($objQuery); 
if($intRows>0)
	{
		echo "<font color='#CB0606'> ID Name นี้มึคนอื่นใช้แล้วครับ</font>";
	}
	else
	{
		echo "<font color='#008000'>  ".$_POST["User"]."  ยังว่างอยู่ครับ</font> ";
	}
		mysql_close
?>