planner: fix mock mpp store will output none data for count(empty-set)

[AilinKid]

What problem does this PR solve?

Issue Number: close #50893

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

[tiprow]

Hi @AilinKid. Thanks for your PR.

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[codecov]

Codecov Report

Merging #50856 (d3db647) into master (7cdab19) will increase coverage by 1.3821%.
Report is 567 commits behind head on master.
The diff coverage is 57.8947%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #50856        +/-   ##
================================================
+ Coverage   70.5964%   71.9786%   +1.3821%     
================================================
  Files          1466       1468         +2     
  Lines        434131     451819     +17688     
================================================
+ Hits         306481     325213     +18732     
+ Misses       108495     105749      -2746     
- Partials      19155      20857      +1702     

Flag	Coverage Δ
integration	31.0246% <57.8947%> (?)

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

Components	Coverage Δ
dumpling	54.2940% <ø> (ø)
parser	∅ <ø> (∅)
br	56.5777% <ø> (+10.7744%)	⬆️

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-02-02 08:24:53.593561108 +0000 UTC m=+1726735.157858799: ☑️ agreed by guo-shaoge.
• 2024-02-02 09:54:43.482976829 +0000 UTC m=+1732125.047274520: ☑️ agreed by qw4990.

[tiprow]

@AilinKid: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
tiprow_fast_test	2c627ac	link	true	/test tiprow_fast_test

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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• OWNERS [guo-shaoge,hawkingrei,qw4990]

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[AilinKid]

/retest

[tiprow]

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

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/retest

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[ti-chi-bot]

@AilinKid: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-mysql-client-test	d3db647	link	true	/test pull-mysql-client-test
idc-jenkins-ci-tidb/mysql-test	d3db647	link	true	/test mysql-test
idc-jenkins-ci-tidb/check_dev	d3db647	link	true	/test check-dev
idc-jenkins-ci-tidb/unit-test	d3db647	link	true	/test unit-test

Full PR test history. Your PR dashboard.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.