Opened 4 years ago

Last modified 4 years ago

#32155 closed New feature

Count() by default uses group by — at Initial Version

Reported by: Sukhinder Mann Owned by: nobody
Component: Database layer (models, ORM) Version: 2.2
Severity: Normal Keywords:
Cc: sukhinder.mann@… Triage Stage: Unreviewed
Has patch: no Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

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.

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:

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.

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