#34992: MariaDB does not support functional group by dependencies
-------------------------------------+-------------------------------------
Reporter: Matthew | Owner: nobody
Somerville |
Type: Bug | Status: new
Component: Database | Version: 4.2
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Requested to be opened from comment 11 on #34978. If you're using MariaDB
with ONLY_FULL_GROUP_BY turned on, all queries that end up using a `GROUP
BY` fail. Given a model such as:
{{{#!python
class Author(models.Model):
pass
class Play(models.Model):
title = models.CharField(max_length=100)
authors = models.ManyToManyField(Author)
}}}
Then `list(Play.objects.annotate(Count('authors')))` generates the SQL:
{{{#!sql
SELECT app_play.id, app_play.title, COUNT(app_play_authors.author_id) AS
authors__count
FROM app_play
LEFT OUTER JOIN app_play_authors ON (app_play.id =
app_play_authors.play_id)
GROUP BY app_play.id
ORDER BY NULL
}}}
Which errors with `django.db.utils.OperationalError: (1055,
"'mariadbtest.app_play.title' isn't in GROUP BY")`
Unlike MySQL since 5.7.5 (release notes: "MySQL now recognizes when a
nonaggregated selected column is functionally dependent on (uniquely
determined by) GROUP BY columns."), MariaDB does not support this feature.
But Django 4.2 assumes both MySQL and MariaDB support it.
Simon's comment on #34978 said: "The solution will likely be to turn off
the allows_group_by_selected_pks feature on MariaDB when
ONLY_FULL_GROUP_BY mode is turned on. Note that the
allows_group_by_selected_pks feature is different from the
allows_group_by_pk feature removed in
041551d716b69ee7c81199eee86a2d10a72e15ab."
--
Ticket URL: <https://code.djangoproject.com/ticket/34992>
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