planner: Add variable for no_decorrelate in select list (#63204)

[ti-chi-bot]

This is an automated cherry-pick of #63204

What problem does this PR solve?

Issue Number: close #51116

Problem Summary:

What changed and how does it work?

Customer requirement to allow decorrelation of subqueries in the select list. Added a variable to control this behavior.

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

[ti-chi-bot]

@terry1purcell This PR has conflicts, I have hold it.
Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

[ti-chi-bot]

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[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 5 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release-8.5@96f2cf5). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #63541   +/-   ##
================================================
  Coverage               ?   57.2717%           
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  Lines                  ?     632558           
  Branches               ?          0           
================================================
  Hits                   ?     362277           
  Misses                 ?     245904           
  Partials               ?      24377           

Flag	Coverage Δ
integration	37.0527% <87.5000%> (?)
unit	72.7647% <87.5000%> (?)

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

Components	Coverage Δ
dumpling	52.9278% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	52.8138% <0.0000%> (?)

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[terry1purcell]

/unhold

[fixdb]

+1

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-09-19 22:29:31.248648306 +0000 UTC m=+50181.319141984: ☑️ agreed by terry1purcell.
• 2025-09-20 05:15:40.387407021 +0000 UTC m=+74550.457900710: ☑️ agreed by fixdb.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fixdb, terry1purcell, yudongusa

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Needs approval from an approver in each of these files:

• OWNERS [fixdb]
• pkg/planner/OWNERS [fixdb,terry1purcell]
• pkg/sessionctx/variable/OWNERS [yudongusa]

Approvers can indicate their approval by writing /approve in a comment
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