expression: limit valid decimal length (#28466)

[ti-srebot]

cherry-pick #28466 to release-5.2
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/28649

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/tidb.git pr/28649:release-5.2-a18e05d2f7f9

---

What problem does this PR solve?

Issue Number: close pingcap/tiflash#3091

Problem Summary:

What is changed and how it works?

Proposal: xxx

What's Changed:

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

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• LittleFall
• ichn-hu

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

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[ti-srebot]

/run-all-tests

[ti-srebot]

@fzhedu you're already a collaborator in bot's repo.

[zimulala]

Please fix conflicts @fzhedu

[LittleFall]

merge

[fzhedu]

/merge

[ti-chi-bot]

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

Commit hash: d0891a5

[fzhedu]

/merge

[fzhedu]

/run-check_dev

[fzhedu]

/run-check_dev

[zhouqiang-cl]

/merge

[zhouqiang-cl]

/merge

[zhouqiang-cl]

/merge

[zhouqiang-cl]

/merge

[ti-chi-bot]

@ti-srebot: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

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