#32155: Count() by default uses group by
-------------------------------------+-------------------------------------
Reporter: Sukhinder Mann | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version: 2.2
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | 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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Description changed by Sukhinder Mann:
Old description:
> I am trying to use Count() with Case to find out multiple conditional
> counts, and count keeps using `id` as default group by. I don't want it
> to use `GROUP BY` by default.
>
> {{{#!python
> Staff.objects.filter(department__id__in=[2,3]).annotate(
> number_of_managers_in_UK=Sum(
> Case(
> When(position="MANAGER", location="UK", then=1),
> output_field=IntegerField(),
> )
> ),
> number_of_directors_in_USA=Sum(
> Case(
> When(position="DIRECTOR", location="USA",
> then=1),
> output_field=IntegerField(),
> )
> )
> )
> }}}
>
> Which creates a SQL query something like this:
>
> {{{#!sql
> SELECT "staff"."id",
> "staff"."location",
> "staff"."position",
> "staff"."salary",
> "staff"."date_of_birth",
> COUNT(
> CASE
> WHEN "staff"."position" = MANAGER AND "staff"."location" = UK
> THEN 1
> ELSE NULL
> END
> ) AS "number_of_managers_in_UK",
> COUNT(
> CASE
> WHEN "staff"."position" = DIRECTOR AND "staff"."location" =
> USA THEN 1
> ELSE NULL
> END
> ) AS "number_of_directors_in_USA"
> FROM "staff"
> WHERE "staff"."department_id" IN (2, 3)
> GROUP BY "staff"."id"; -- This group by is unnecessary and spoils the
> result set
> }}}
>
> Even though `Count` is an Aggregator function in SQL it can be used
> without `GROUP BY`. It would be good if we can have either a parameter or
> something to specify whether to use group by or not instead of defaulting
> to `GROUP BY`.
New description:
I am trying to use Count() with Case to find out multiple conditional
counts, and count keeps using `id` as default group by. I don't want it to
use `GROUP BY` by default.
{{{#!python
Staff.objects.filter(department__id__in=[2,3]).annotate(
number_of_managers_in_UK=Sum(
Case(
When(position="MANAGER", location="UK", then=1),
output_field=IntegerField(),
)
),
number_of_directors_in_USA=Sum(
Case(
When(position="DIRECTOR", location="USA", then=1),
output_field=IntegerField(),
)
)
)
}}}
Which creates a SQL query something like this:
{{{#!sql
SELECT "staff"."id",
"staff"."location",
"staff"."position",
"staff"."salary",
"staff"."date_of_birth", -- I don't want all these other attributes as
well but I can't get rid of these as well, I just need the count
attributes
COUNT(
CASE
WHEN "staff"."position" = MANAGER AND "staff"."location" = UK
THEN 1
ELSE NULL
END
) AS "number_of_managers_in_UK",
COUNT(
CASE
WHEN "staff"."position" = DIRECTOR AND "staff"."location" =
USA THEN 1
ELSE NULL
END
) AS "number_of_directors_in_USA"
FROM "staff"
WHERE "staff"."department_id" IN (2, 3)
GROUP BY "staff"."id"; -- This group by is unnecessary and spoils the
result set
}}}
Even though `Count` is an Aggregator function in SQL it can be used
without `GROUP BY`. It would be good if we can have either a parameter or
something to specify whether to use group by or not instead of defaulting
to `GROUP BY`.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/32155#comment:2>
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