planner: Set minimum cost to avoid parent multiplication cost discrepancies (#56387)

[ti-chi-bot]

This is an automated cherry-pick of #56387

What problem does this PR solve?

Issue Number: ref #55126

Problem Summary:

What changed and how does it work?

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]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, Rustin170506

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-09-30 06:49:42.051574273 +0000 UTC m=+251137.471787282: ☑️ agreed by hawkingrei.
• 2024-09-30 06:55:54.169380715 +0000 UTC m=+251509.589593727: ☑️ agreed by Rustin170506.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (release-7.5@3edb7a3). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.5     #56412   +/-   ##
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  Coverage               ?   72.0205%           
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  Files                  ?       1415           
  Lines                  ?     412513           
  Branches               ?          0           
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  Hits                   ?     297094           
  Misses                 ?      95523           
  Partials               ?      19896           

Flag	Coverage Δ
unit	72.0205% <100.0000%> (?)

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

Components	Coverage Δ
dumpling	52.9400% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	53.5488% <0.0000%> (?)