Index hint for nested queries (bound to alias)

[VladimirKuzmin]

Summary:

Index hint should remember which table it was applied.
Solution:

• on each aliases changing in query also change alias in index hint
• at rewriting stage modify SQL according the alias

Checklist:

• Docs updated, or N/A
• Line added to HISTORY.rst, or N/A
• Added extra items to checklist as applicable
• All commits squashed into one.

Test Plan:

• added tests for nested queries up to 3 level generated by Django ORM
• added test for raw SQL query

Known issue:
For nested queries like this (without any JOIN):

SomeModel.objects.filter(pk__in=SomeModel.objects.all())

Django will not assign alias to any table, so index hint will be always applied to outer query.
But it looks like queries like this are useless.

[adamchainz]

This is nice and looks good. A quick glance doesn't reveal anything problematic, but I'll give it a bit more testing during the week!

[thebarbershop]

Can someone share the status of this patch? Is the issue addressed by some other PR, or is it just left unfixed for some reason?

[adamchainz]

I've been meaning to review this but it's quite a big chunk of stuff to understand at once (and after this time, rebase). And I've never had the issue myself, and I guess I've always had higher impact things to work on.

If you want to rebase it that would be a helpful start; even more helpful would be running it in your app (dev, or staigng, or even prod) and seeing if you encounter any issues not addressed by tests.

[thebarbershop]

Thanks for the update, Adam!

I'm currently working to upgrade a project from ancient times (Django 1.9 + A forked django-mysql 1.0.9 with this PR applied) so I can't contribute to the upstream at this point. But I'll be happy to return to this issue when I can.