python – Django注释总和的平均值(1.6.5)

目前试图获取一个组的平均值,但当我尝试执行正确的查询集时,它会抱怨语法不正确

objs = MyModel.objects.filter(...).values('user','value')
objs = objs.annotate(sum=Sum('value')) 
# i've also tried adding `.values('sum')` to the above
objs = objs.aggregate(Avg('sum')) # whines here

有没有办法在不放弃sql的情况下执行此操作？所需的sql就是这样的

SELECT AVG(`sum`) as `avg` FROM ( 
    SELECT SUM(`appname_mymodel`.`value`) AS `sum`
    FROM `appname_mymodel` 
    GROUP BY 
        `appname_mymodel`.`user_id`,`appname_mymodel`.`value`
) as subquery ORDER BY NULL;

不确定django是否适合子查询.

这是错误消息：

ProgrammingError: (1064,"You have an error in your sql Syntax; check the manual that corresponds to your MysqL server version for the right Syntax to use near 'FROM (SELECT SUM(`appname_mymodel`.`value`) AS `sum` FROM `appname_' at line 1")

Django版本 – 1.6.5

MysqL版本 – 5.5

笔记：

>如果我省略了值(分组依据),它可以正常工作(即objs.filter(…).annotate(…).aggregate(…)
>以下示例足以作为完全可重复的示例.

模型：

# Create your models here.

class UserProfile(models.Model):
    name = models.CharField(max_length=200)

class OtherFK(models.Model):
    name = models.CharField(max_length=200)

class MyModel(models.Model):
    # Happens if value is CharField or IntegerField
    value = models.CharField(max_length=200,blank=True,null=True)
    date = models.DateField()
    user = models.ForeignKey(UserProfile)
    other_fk = models.ForeignKey(OtherFK)

例：

>>> from app_name.models import UserProfile,OtherFK,MyModel
>>> up = UserProfile.objects.create(name="test")
>>> fk = OtherFK.objects.create(name="test")
>>> v1 = MyModel.objects.create(user=up,other_fk=fk,value="12",date="2015-10-01")
>>> v2 = MyModel.objects.create(user=up,value="13",date="2015-10-02")
>>> from django.db.models import Sum,Avg
>>> MyModel.objects.all().values("user").distinct().annotate(sum=Sum("value")).aggregate(Avg('sum'))
ProgrammingError: (1064,"You have an error in your sql Syntax; check the manual that corresponds to your MysqL server version for the right Syntax to use near 'FROM (SELECT disTINCT `app_name_mymodel`.`user_id` AS `user_id`,SUM(`app_name_m' at line 1")
>>> MyModel.objects.all().values("user").distinct().annotate(sum=Sum("value"))
[{'sum': 25.0,'user': 1L}]
>>> print MyModel.objects.all().values("user").distinct().annotate(sum=Sum("value")).query
SELECT disTINCT `app_name_mymodel`.`user_id`,SUM(`app_name_mymodel`.`value`) AS `sum` FROM `app_name_mymodel` GROUP BY `app_name_mymodel`.`user_id` ORDER BY NULL

解决方法

我认为这就是您所需要的,请在测试下面的一行后给出反馈：

MyModel.objects.filter(...).values('user__id').distinct().annotate(sum=Sum('value')).aggregate(Avg('sum'))