如何在 Django ORM 中执行 GROUP BY ... COUNT 或 SUM？

Question

序言：

这是SO中经常出现的问题：

Django Models Group By
Django equivalent for count and group by
How to query as GROUP BY in django?
How to use the ORM for the equivalent of a SQL count, group and join query?

我已经在 SO 文档中编写了一个示例，但由于该文档将于 2017 年 8 月 8 日关闭，我将遵循 this widely upvoted and discussed meta answer 的建议并将我的示例转换为自我回答 post.

当然，我也很乐意看到任何不同的方法！！

问题：

假设模型：

class Books(models.Model):
    title  = models.CharField()
    author = models.CharField()
    price = models.FloatField()

如何使用 Django ORM 对该模型执行以下查询：

GROUP BY ... COUNT:

SELECT author, COUNT(author) AS count
FROM myapp_books GROUP BY author

GROUP BY ... SUM:

SELECT author,  SUM (price) AS total_price
FROM myapp_books GROUP BY author

Answer 1

我们可以在 Django ORM 上执行 GROUP BY ... COUNT 或 GROUP BY ... SUM SQL 等效查询，使用 annotate(), values(), the django.db.models's Count and Sum methods respectfully and optionally the order_by() 方法：

分组依据...计数：

 from django.db.models import Count

 result = Books.objects.values('author')
                       .order_by('author')
                       .annotate(count=Count('author'))

现在结果包含一个字典和两个键：author 和 count:

   author    | count
 ------------|-------
  OneAuthor  |   5
 OtherAuthor |   2
    ...      |  ...

分组依据...总和：

 from django.db.models import Sum

  result = Books.objects.values('author')
                        .order_by('author')
                        .annotate(total_price=Sum('price'))

现在结果包含一个字典，其中有两列：author 和 total_price:

   author    | total_price
 ------------|-------------
  OneAuthor  |    100.35
 OtherAuthor |     50.00
     ...     |      ...

2021 年 4 月 13 日更新

正如@dgw 在评论中指出的那样，在模型使用元选项对行进行排序的情况下（例如 ordering), the order_by() 子句 是最重要的 聚合成功！

Answer 2

在 SUM() 分组中，你几乎可以得到两个字典对象，比如

inv_data_tot_paid =Invoice.objects.aggregate(total=Sum('amount', filter=Q(status = True,month = m,created_at__year=y)),paid=Sum('amount', filter=Q(status = True,month = m,created_at__year=y,paid=1)))
print(inv_data_tot_paid)
##output -{'total': 103456, 'paid': None}

不要尝试超过两个查询过滤器否则，你会得到类似

的错误

如何在 Django ORM 中执行 GROUP BY ... COUNT 或 SUM？

How to execute a GROUP BY ... COUNT or SUM in Django ORM?

python

django

group-by

django-orm