#34206: annotation of another annotation duplicate query rule
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Reporter: Mohammad99k | Owner: nobody
Type: Cleanup/optimization | Status: new
Component: Uncategorized | Version: 4.1
Severity: Normal | Keywords: annotate
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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When I use an annotation in another annotation, query is duplicated like
bellow:
{{{
groups =
StudyGroup.objects.filter(group_filter).select_related('parent').annotate(
no_members=Count('student', distinct=True),
point=Sum('student__point__point', filter=point_filter),
avg_point=ExpressionWrapper(F('point') / F('no_members'),
output_field=FloatField()))
}}}
In above queryset, {{{Count('student', distinct=True)}}} calculate for
no_members and when I use no_members in avg_point annotation again query
calculate {{{Count('student', distinct=True)}}} instead of use no_members
directly.
{{{
COUNT(DISTINCT `users_student`.`user_id`) AS `no_members`,
SUM(`study_league_point`.`point`) AS `point`,
(
SUM(`study_league_point`.`point`) / COUNT(DISTINCT
`users_student`.`user_id`)
) AS `avg_point`,
}}}
In above my SQL code {{{COUNT(DISTINCT `users_student`.`user_id`)}}} is
duplicate ({{{SUM(`study_league_point`.`point`)}}} too).
my desired query is like this:
{{{
COUNT(DISTINCT `users_student`.`user_id`) AS `no_members`,
SUM(`study_league_point`.`point`) AS `point`,
(
point / no_members
) AS `avg_point`,
}}}
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Ticket URL: <https://code.djangoproject.com/ticket/34206>
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