planner: extend order ratio to joins | tidb-test=pr/2530

[terry1purcell]

What problem does this PR solve?

Issue Number: close #62034

Problem Summary:

What changed and how does it work?

Increases the scope of variable tidb_opt_ordering_index_selectivity_ratio to apply to index joins - where the ordering is provided on the leading table of the join, but the filtering is on subsequent tables in the join query.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[tiprow]

Hi @terry1purcell. Thanks for your PR.

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[terry1purcell]

/retest-required

[tiprow]

@terry1purcell: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

/retest-required

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[terry1purcell]

/ok-to-test

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.3633%. Comparing base (1962f22) to head (32d6e1d).
Report is 2 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #61687        +/-   ##
================================================
+ Coverage   72.9246%   73.3633%   +0.4386%     
================================================
  Files          1739       1739                
  Lines        482820     482850        +30     
================================================
+ Hits         352095     354235      +2140     
+ Misses       109169     107052      -2117     
- Partials      21556      21563         +7     

Flag	Coverage Δ
integration	42.3452% <100.0000%> (?)
unit	72.2026% <100.0000%> (+0.0460%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	52.7804% <ø> (ø)
parser	∅ <ø> (∅)
br	46.3204% <ø> (-0.0154%)	⬇️

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-06-28 15:30:26.94517626 +0000 UTC m=+1149679.668355235: ☑️ agreed by time-and-fate.
• 2025-07-01 01:21:16.424023893 +0000 UTC m=+1357929.147202874: ☑️ agreed by hawkingrei.

[yudongusa]

Please also open a document PR

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, time-and-fate, yudongusa

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Needs approval from an approver in each of these files:

• pkg/bindinfo/OWNERS [hawkingrei,time-and-fate]
• pkg/planner/OWNERS [hawkingrei,time-and-fate]
• pkg/sessionctx/variable/OWNERS [yudongusa]

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[terry1purcell]

/cherry-pick release-8.5

[ti-chi-bot]

@terry1purcell: new pull request created to branch release-8.5: #62155.
But this PR has conflicts, please resolve them!

In response to this:

/cherry-pick release-8.5

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