Opened 2 years ago
Last modified 19 months ago
#33759 closed Cleanup/optimization
Using subquery to filter a model delete creates sub-optimal SQL — at Initial Version
Reported by: | Christofer Bertonha | Owned by: | |
---|---|---|---|
Component: | Database layer (models, ORM) | Version: | 4.0 |
Severity: | Normal | Keywords: | |
Cc: | Simon Charette | Triage Stage: | Ready for checkin |
Has patch: | yes | Needs documentation: | no |
Needs tests: | no | Patch needs improvement: | no |
Easy pickings: | no | UI/UX: | no |
Description
Taking in consideration the app of tutorial for demonstrate the issue.
using postgresql as db.
Executing this following code:
subquery = Comment.objects.filter(created_at__lt=datetime(2022, 6, 1))[:1000] Comment.objects..filter(id__in=subquery).delete()
Generates the following SQL:
DELETE FROM "comment" WHERE "comment"."id" IN (SELECT V0."id" FROM "comment" V0 WHERE V0."id" IN (SELECT U0."id" FROM "comment" U0 WHERE U0."created_at" < \'2022-06-01T00:00:00+00:00\'::timestamptz LIMIT 1000))
The inner select V0 is completely unnecessary
If a simple select with the same subquery is executed. It generates expected SQL query.
subquery = Comment.objects.filter(created_at__lt=datetime(2022, 6, 1))[:1000] comments = list( Comment.objects..filter(id__in=subquery) )
SELECT * FROM "comment" WHERE "comment"."id" IN (SELECT U0."id" FROM "comment" U0 WHERE U0."created_at" < '2022-06-01T00:00:00+00:00'::timestamptz LIMIT 1000),
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