为什么我从 Django 查询中收到此 sql 语法错误？

Question

In Django I have the following queries in a view

applicant=Applicants.objects.get(ben=entity_number)
f471s=applicant.form471_set.order_by("-funding_year","number")
enrollment=f471s.values("schooldata__ben").annotate(f=Max("number")).filter(
           number=F("f")).values().aggregate(
           s=Sum("schooldata__student_count"))['s']

When I try to access the page for that view, I get the error

DatabaseError
(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 `frontend_form471`.`number` AS `number`,
`frontend_form471`.`form_s' at line 1")

I had the logger print out the SQL that Django is generating and I got

(0.001) SELECT  FROM (SELECT `frontend_form471`.`number` AS `number`,
`frontend_form471`.`form_status` AS `form_status`, `frontend_form471`.`ben_id`
AS `ben_id`, `frontend_form471`.`funding_year` AS `funding_year`,
MAX(`frontend_form471`.`number`) AS `f` FROM `frontend_form471` LEFT OUTER JOIN
`SchoolData` ON (`frontend_form471`.`number` = `SchoolData`.`f471 Application Number`)
WHERE (`frontend_form471`.`ben_id` = 122871 ) GROUP BY `frontend_form471`.`number`,
`frontend_form471`.`number`, `frontend_form471`.`form_status`,
`frontend_form471`.`ben_id`, `frontend_form471`.`funding_year` HAVING
`frontend_form471`.`number` =  MAX(`frontend_form471`.`number`) ORDER BY
`frontend_form471`.`funding_year` DESC, `frontend_form471`.`number` ASC) 
subquery; args=(u'122871',)

For reference, I am using MySQL 5.1.54-1ubuntu4. It looks like the syntax error is in the first line, but I do not understand why Django is generating SQL code with improper syntax. Is there any way I can change something (a setting, possibly) to fix this?

Edit: in response to an answer, I also tried running the third line of python code without the second .values() call and got exactly the same effect.

Answer 1

In case other folks are wondering as I was, this is an accepted Django bug: https://code.djangoproject.com/ticket/15624

Answer 2

I ended up avoiding the problem by replacing my third line of python code with:

latest=SchoolData.objects.filter(f471__ben=entity_number).values(
       'ben').annotate(m=Max('f471__number')).order_by().distinct()
enrollment=sum(SchoolData.objects.filter(ben=l['ben']).get(
           f471__number=l['m']).student_count for l in latest)

This worked but it was very slow. In the end some extra information about my data allowed me to optimize like this:

latestYear=f471s.aggregate(m=Max('funding_year'))['m']
enrollment=SchoolData.objects.filter(f471__ben=entity_number,
           f471__funding_year=latestYear).distinct().aggregate(
           s=Sum('student_count'))['s']

which does not do exactly the same thing but solved my particular problem better.

Answer 3

The issue is the second empty values() clause after the annotate. You're literally telling django not to include any columns in the select.