Opened 3 years ago

Closed 6 weeks ago

Last modified 6 weeks ago

#20888 closed New feature (fixed)

Allow defining order of column for indexes

Reported by: anonymous Owned by: Akshesh Doshi
Component: Database layer (models, ORM) Version: master
Severity: Normal Keywords: index, order, db-indexes
Cc: aksheshdoshi@… Triage Stage: Accepted
Has patch: yes Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

Description (last modified by Tim Graham)

Hi,

Currently the index_together tuples do not support index ordering using + / -.

If I have the following table:

class Messages:
   user_id,
   rating,
   last_update,

   index_together=[
     ['user_id', 'rating',  'last_update',] # sorted ASC by default
  ]

So for MySQL, the following query cannot make use of the index:

Messages.objects.filter(user_id=xxx).order_by('+rating','-last_update')

Pardon me if it actually can make use of the index.

I know there are workarounds, such as negating values to make a DESC ordering become ASC ordering.
But it is just nice to have such a feature.
Btw, what is the reason for not having this feature?

Change History (15)

comment:1 Changed 3 years ago by wim@…

Needs documentation: unset
Needs tests: unset
Patch needs improvement: unset

Hi anonymous, thanks for taking the time to fill in a ticket. Just to answer your question: most features are not implemented because people did not have time to write the code for it. :) So if you are willing to write a pull request and contribute such a feature could land in Django.

Unfortunately I do not understand MySQl enough to mark this ticket as accepted.

comment:2 Changed 3 years ago by Anssi Kääriäinen

Triage Stage: UnreviewedAccepted

To me this seems acceptable. Of course, supporting this only on MySQL isn't good, I believe most backends support index ordering.

comment:3 Changed 3 years ago by Daniel Boeve

Owner: changed from nobody to Daniel Boeve
Status: newassigned

comment:4 Changed 3 years ago by Tim Graham

Easy pickings: unset

comment:5 Changed 3 years ago by anonymous

Easy pickings: set
Owner: Daniel Boeve deleted
Status: assignednew

comment:6 Changed 3 years ago by Tim Graham

Easy pickings: unset

comment:7 Changed 7 months ago by Akshesh Doshi

Cc: aksheshdoshi@… added

comment:8 Changed 7 months ago by Asif Saifuddin Auvi

Version: 1.5master

comment:9 Changed 5 months ago by Tim Graham

Description: modified (diff)
Keywords: db-indexes added

comment:10 Changed 2 months ago by Akshesh Doshi

Owner: set to Akshesh Doshi
Status: newassigned

comment:11 Changed 2 months ago by Akshesh Doshi

Has patch: set

PR: https://github.com/django/django/pull/6982

Although requested for alter_index_together, I have implemented the feature with the new class based indexes which would allow users to do the same thing.

The patch contains implementation for all databases except MySQL which doesn't support the feature itself according to their official docs. I felt this to be a bit weird as originally the feature had been requested specifically for MySQL. Please let me know if I missed something in this context.

The patch doesn't add the feature for unique_together as I couldn't understand/don't know what that means. I can try to add it for unique_together as well if somebody could explain that.

Last edited 7 weeks ago by Akshesh Doshi (previous) (diff)

comment:12 Changed 8 weeks ago by Tim Graham

Summary: Index ordering in index_together and unique_togetherIndex ordering in index_together

I'll retitle the ticket and we can open a new one if there's more to be done with respect to unique_together.

comment:13 Changed 7 weeks ago by Tim Graham <timograham@…>

In f842d10:

Refs #20888 -- Added index order introspection.

comment:14 Changed 6 weeks ago by Tim Graham <timograham@…>

Resolution: fixed
Status: assignedclosed

In 311a8e8:

Fixed #20888 -- Added support for column order in class-based indexes.

comment:15 Changed 6 weeks ago by Akshesh Doshi

Summary: Index ordering in index_togetherAllow defining order of column for indexes

Since technically we haven't fixed the ticket described by the earlier summary, but in the end it's the feature that matters so won't reopen this and renaming it instead.

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