当外键没有返回任何内容时，如何在MySQL中选择记录？

SELECT videos.id, videos.game_id, videos.xbox360, videos.ps3, videos.pc,
  videos.wii, videos.other, videos.thumbnail, videos.vid_info, videos.sdvid,
  videos.hdvid, UNIX_TIMESTAMP( videos.date_added ) , game_data.name, 
  AVG( video_ratings.rating )
FROM videos, game_data, video_ratings
WHERE videos.game_id = game_data.id
  AND videos.id = video_ratings.video_id
GROUP BY videos.id, video_ratings.video_id
ORDER BY videos.date_added DESC LIMIT 10;
SELECT videos.id, videos.game_id, videos.xbox36