planner: use the correct fraction for decimal values in plan cache

[qw4990]

What problem does this PR solve?

Issue Number: close #43311

Problem Summary: planner: use the correct fraction for decimal values in plan cache

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

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]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• chrysan
• hawkingrei

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[qw4990]

/test tiflash-ghpr-integration-tests

[ti-chi-bot]

@qw4990: The specified target(s) for /test were not found.
The following commands are available to trigger required jobs:

• /test build
• /test check-dev
• /test check-dev2
• /test mysql-test
• /test unit-test

Use /test all to run all jobs.

In response to this:

/test tiflash-ghpr-integration-tests

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[qw4990]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: c46b9ec

[qw4990]

/cherry-pick release-7.1

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #43331.

[ti-chi-bot]

@qw4990: new pull request could not be created: failed to create pull request against pingcap/tidb#release-7.1 from head ti-chi-bot:cherry-pick-43329-to-release-7.1: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"A pull request already exists for ti-chi-bot:cherry-pick-43329-to-release-7.1."}],"documentation_url":"https://docs.github.com/rest/reference/pulls#create-a-pull-request"}

In response to this:

/cherry-pick release-7.1

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 ti-community-infra/tichi repository.