After that create a php file to generate the xml data and named it as get_data_xml.php. Put the PHP code as shown below:

require('../path to your file/cls_generateXml.php');
header('Content-type: text/xml');
$param = json_decode(str_replace('\\','',$_POST['param']));
$dataList = doGetData($param);
try {
	/*** a new dom object ***/
	$dom = new domDocument;
	/*** make the output tidy ***/
	$dom--->formatOutput = true;
	/*** create the root element ***/
	$dom->appendChild($dom->createElement( "xmlData" ));
	
	/*** create the simple xml element ***/
	$sxe = simplexml_import_dom( $dom );
	
	if(!empty($dataList)) {
		foreach($dataList as $key => $value) {
			$index = $sxe->addChild("index");
			$index->userId = $value['id']; 
		}
	}

	/*** show the xml ***/
	echo $sxe->asXML();
}
catch( Exception $e ) { echo $e->getMessage(); }

function doGetData($param) {
	$obj = new cls_generateXml();
	$dataList = $obj->getData($param);
	return $dataList; 
}

Create another php file and named it as cls_generateXml.php. This file is used to get data from database.

class cls_generateXml {
	public function dbConnect() {
		host = 'your host name';
		user = 'username';
		password = 'password';
		dbName = 'database name';
		$link = mysqli_connect(host, user, password, dbName); mysqli_select_db($link,dbName); mb_language('uni'); 	
		mb_internal_encoding('UTF-8');
		mysqli_query( $link,"SET character_set_results=utf8");
		mysqli_query( $link,"SET character_set_server=utf8");
		mysqli_query( $link,"SET character_set_database=utf8");
		mysqli_query( $link,"set names 'utf8'"); return $link; 
	}
	
	public function getData(param) {
		$con = $this->dbConnect();
		$sql = " SELECT * FROM tbl_data WHERE id = '".param['id']."' ";
		$query = mysqli_query($con,$sql);
		if (!$query) { die(mysqli_error($con)); }
		while($result = mysqli_fetch_assoc($query)) {
			$dataList[] = $result; 
		}
		mysqli_close($con); 
		return $dataList; 
	} 
}