planner: fix unique key get wrong row count when to query the NULL value | tidb-test=pr/2476

[ti-chi-bot]

This is an automated cherry-pick of #56117

What problem does this PR solve?

Issue Number: close #56116

Problem Summary:

What changed and how does it work?

There will be issues with the row count under index/unique index. Previously, we would uniformly count the row count for this PointGet as 1, but if it is null, it will no longer be 1 and must be calculated according to the null count.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

From internal test cases

• 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

[hawkingrei]

/retest

[hawkingrei]

/retest

[hawkingrei]

/retest

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (release-6.5@116ffee). Learn more about missing BASE report.

Additional details and impacted files

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##             release-6.5     #56277   +/-   ##
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  Misses                 ?      76382           
  Partials               ?      16735           

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, qw4990

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-02-05 09:22:43.623955725 +0000 UTC m=+263635.156367721: ☑️ agreed by hawkingrei.
• 2025-02-05 11:01:18.419943021 +0000 UTC m=+269549.952355020: ☑️ agreed by qw4990.