statistics: use slices to simple code

[hawkingrei]

What problem does this PR solve?

Issue Number: ref #45933

Problem Summary:

What is changed and how it works?

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 NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please ask for approval from hawkingrei. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

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

[codecov]

Codecov Report

Merging #47025 (fdd1e7b) into master (bf173eb) will decrease coverage by 0.3893%.
Report is 2 commits behind head on master.
The diff coverage is 66.6666%.

❗ Current head fdd1e7b differs from pull request most recent head 4ea1a7c. Consider uploading reports for the commit 4ea1a7c to get more accurate results

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #47025        +/-   ##
================================================
- Coverage   73.0800%   72.6907%   -0.3893%     
================================================
  Files          1335       1353        +18     
  Lines        398099     403706      +5607     
================================================
+ Hits         290931     293457      +2526     
- Misses        88417      91608      +3191     
+ Partials      18751      18641       -110     

Flag	Coverage Δ
integration	30.1571% <66.6666%> (?)

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

Components	Coverage Δ
dumpling	53.9913% <ø> (ø)
parser	84.9980% <ø> (ø)
br	48.5650% <ø> (-4.3434%)	⬇️

[tiprow]

@hawkingrei: 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	7d9db25	link	true	/test tiprow_fast_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.

[ti-chi-bot]

@hawkingrei: 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
idc-jenkins-ci-tidb/mysql-test	7d9db25	link	true	/test mysql-test
idc-jenkins-ci-tidb/unit-test	4ea1a7c	link	true	/test unit-test
idc-jenkins-ci-tidb/check_dev_2	4ea1a7c	link	true	/test check-dev2
idc-jenkins-ci-tidb/check_dev	4ea1a7c	link	true	/test check-dev

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.