Django-SQLite与MySQL上的DateTimeField查询

此查询在MySQL中返回一个空查询集,但在SQLite中有效:

commented_this_month = Post.objects.filter(comment__created__month=now.month)

我的模型非常简单:

class Comment(models.Model):
    comment = models.TextField()
    author = models.ForeignKey(User, on_delete=models.CASCADE)
    created = models.DateTimeField(default=timezone.now)
    post = models.ForeignKey(Post, on_delete=models.CASCADE)

我有什么遗漏吗?