inserting data in mysql previously defined variables

inserting data in mysql previously defined variables

I am using this code to get data from Json and insert them to mysql.
However it inserts no records in the data base.
<?php
include("db.php");
$currsiteurl = 'http://graph.facebook.com/1597233119';
$graph = json_decode(file_get_contents($currsiteurl));
$id = $graph->id;
echo "id : ".$id;
echo "<br>";
$username = $graph->username;
echo "username : ".$username;
echo "<br>";
$gender = $graph->gender;
echo "gender : ".$gender;
echo "<br>";
$locale = $graph->locale;
echo "locale : ".$locale;
mysql_query("INSERT INTO users_data (id, username, gender, locale)
VALUES ('.$id', '.$username', '.$gender', '.$locale')");
?>
Can any one show me whereis the mistake ?