//get all id's of ur friend that has installed your application
 $friend_pics=$facebook->api( array( 'method' => 'fql.query', 'query' => "SELECT uid FROM user WHERE uid   IN(SELECT uid2 from friend WHERE uid1='$user') AND is_app_user = 1" ) ); // this query work fine
//your top10 friends in app
$result="SELECT * FROM fb_user WHERE user_id IN($friend_pics) ORDER BY oldscore DESC LIMIT 0,10";
db_execute($result);

i want to retrive ten top scorer from my database stored in oldscore but in my second query the array name $friend_pics is not working i guess,plz help me thanks