Django 聚合执行过多的 GROUP BY 子句
我正在 MySQL 上使用 Django ORM 进行非常简单的聚合，它生成一个包含 data 字段的 GROUP BY 子句，该字段非常大，并且速度很慢将查询量降低了 100 倍以上。
这是该模型的简化版本：
class Document(models.Model):
data = models.TextField()
class Attachment(models.Model):
document = models.ForeignKey(Document)
我正在运行的查询：
Document.objects.annotate(num_attachments=Count('attachment'))
以及 SQL 输出：
SELECT
`document_document`.`id`,
`document_document`.`data`,
COUNT(`document_attachment`.`id`) AS `num_attachments`
FROM `document_document`
LEFT OUTER JOIN `document_attachment`
ON (`document_document`.`id` = `document_attachment`.`document_id`)
GROUP BY
`document_document`.`id`,
`document_document`.`id`,
`document_document`.`data`
ORDER BY NULL
在数据字段上执行 GROUP BY 是不必要且荒谬的。我可以通过执行 values 查询来阻止此操作：
Document.objects.values('pk').annotate(num_attachments=Count('attachment'))
但是如何获得真实的带注释的文档查询作为结果呢？
I am doing a very simple aggregation using the Django ORM on MySQL, and it is producing a GROUP BY clause that includes the data field, which is very large, and is slowing down the query by over 100-fold.
Here is a simplified version of the model:
class Document(models.Model):
data = models.TextField()
class Attachment(models.Model):
document = models.ForeignKey(Document)
And the query I am running:
Document.objects.annotate(num_attachments=Count('attachment'))
And the SQL output:
SELECT
`document_document`.`id`,
`document_document`.`data`,
COUNT(`document_attachment`.`id`) AS `num_attachments`
FROM `document_document`
LEFT OUTER JOIN `document_attachment`
ON (`document_document`.`id` = `document_attachment`.`document_id`)
GROUP BY
`document_document`.`id`,
`document_document`.`id`,
`document_document`.`data`
ORDER BY NULL
Doing GROUP BY on the data field is unnecessary and ridiculous. I can stop this by doing a values query:
Document.objects.values('pk').annotate(num_attachments=Count('attachment'))
But then how do I get a real, annotated Document query as the result?
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Django 核心提交者 Karen Tracy 已确认这实际上是 Django 中的一个错误：
http://groups.google.com/group/django-users/browse_thread/thread/22d4d46c8646b2c4#
Karen Tracy, a Django core committer, has confirmed that this is actually a bug in Django:
http://groups.google.com/group/django-users/browse_thread/thread/22d4d46c8646b2c4#
https://code.djangoproject.com/ticket/17144