Show multiple marker and polyline between them in google maps - google-maps

Question

Hi i am working on google maps. i have display multiple location markers and want to show polylines between the markers. Markers are shown but polylines are not displayed. Any help will be appreciated.
here is my code to fetch location data from db
<?php
$hostname = 'localhost';
$dbname = 'gtroad';
$username = 'root';
$password = '';
mysql_connect("$hostname", "$username", "$password") or DIE("Connection to host is failed");
mysql_select_db("$dbname") or DIE("database not available");
$q1 = mysql_query("SELECT city, lat, lng FROM location");
$lalng = array();
for($i=0;$i<mysql_num_rows($q1);$i++)
{
$j = 0;
$obj = mysql_fetch_object($q1);
$lalng[$i][$j] = $obj->city;
$j++;
$lalng[$i][$j] = $obj->lat;
$j++;
$lalng[$i][$j] = $obj->lng;
$j++;
}
$ar = json_encode($lalng);
?>
here is javascript code for google map to show markers and polyline between them...
<script>
function initialize() {
var mapOptions = {
zoom: 6,
featureType: 'road',
center: new google.maps.LatLng(30.6667, 72.1667),
mapTypeId: google.maps.MapTypeId.ROADMAP
};
var map = new google.maps.Map(document.getElementById('map-canvas'),
mapOptions);
var locations = <?php echo $ar; ?>;
var infowindow = new google.maps.InfoWindow();
var marker, i;
for (i = 0; i < locations.length; i++) {
marker = new google.maps.Marker({
position: new google.maps.LatLng(locations[i][1], locations[i][2]),
map: map
});
google.maps.event.addListener(marker, 'click', (function(marker, i) {
return function() {
infowindow.setContent(locations[i][0]);
infowindow.open(map, marker);
}
})(marker, i));
}
/* polyline code */
var flightPath, mylatlong = new Array();
for(i=0; i < locations.length; i++){
mylatlong = new google.maps.LatLng(locations[i][1], locations[i][2]);
document.write(mylatlong);
}
flightPath = new google.maps.Polyline({
path: mylatlong,
geodesic: true,
strokeColor: '#999999',
strokeOpacity: 1.0,
strokeWeight: 3
});
flightPath.setMap(map);
} //end polyline code
google.maps.event.addDomListener(window, 'load', initialize);
google.maps.event.addDomListener(window, "resize", function() {
var center = map.getCenter();
google.maps.event.trigger(map, "resize");
map.setCenter(center);
});
</script>