Re: Django aggregation does excessive GROUP BY clauses

On Tue, Nov 1, 2011 at 6:19 PM, christian.oudard <christian.oudard@gmail.com> wrote:

I am doing a very simple aggregation using the Django ORM, 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'))

The SQL generated by the ORM for this query changed between Django version 1.2 and 1.3. The 1.2 SQL did a group by only on the id field. With 1.3 we're getting id twice and then all other fields in the model. Bisection shows the change was made with r14715:

https://code.djangoproject.com/changeset/14715

It certainly looks to me like the old SQL was correct and preferable for this particular case. In a brief search I did not find a ticket reporting this issue -- could you open one?

Karen

--
http://tracey.org/kmt/

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