带有注释的Django queryset,为什么GROUP BY应用于所有字段？

我正在使用带有PostgreSQL的Django 1.6,并有以下型号:

# models.py
class Game(AbstractContentModel, AbstractScoreModel):
    name = models.CharField(_("name"), max_length=100, blank=True)
    developer = models.CharField(_('Developer'), max_length=255)
    distributor = models.CharField(_('Distributor'), max_length=255, blank=True)
    # ...
    reviews = models.ManyToManyField(Review, related_name="games", blank=True, verbose_name=_("Reviews"))
    videos = models.ManyToManyField(Video, related_name="games", blank=True, verbose_name=_("Videos"))
    images = models.ManyToManyField(Image, related_name="games", blank=True, verbose_name=_("Gallery"))

我正在尝试获取所有游戏,并且每个游戏都会添加相关视频,评论和图像,如下所示:

# views.py
qs = Game.objects.all()
qs = qs.annotate(video_count=models.Count('videos'))
qs = qs.annotate(review_count=models.Count('reviews'))
qs = qs.annotate(image_count=models.Count('images'))

结果查询是:

SELECT 
"content_game"."id", 
"content_game"."name",
"content_game"."developer", 
"content_game"."distributor",
COUNT("content_game_videos"."video_id") AS "video_count",
COUNT("content_game_reviews"."review_id") AS "review_count", 
COUNT("content_game_images"."image_id") AS "image_count" 
FROM "content_game" 
LEFT OUTER JOIN "content_game_videos" ON ( "content_game"."id" = "content_game_videos"."game_id" )
LEFT OUTER JOIN "content_game_reviews" ON ( "content_game"."id" = "content_game_reviews"."game_id" ) 
LEFT OUTER JOIN "content_game_images" ON ( "content_game"."id" = "content_game_images"."game_id" ) 
GROUP BY 
"content_game"."id", 
"content_game"."name",
"content_game"."developer", 
"content_game"."distributor";

我的问题是 - 为什么GROUP BY子句中有所有选定的字段？最重要的是,除了原始SQL之外,我怎么能摆脱它们呢？

我知道使用它会很好.values(),但我希望结果查询中的每个字段.如果我只是使用GROUP BY "content_game"."id",结果是一样的,但我不知道如何使用它与Django ORM一样.