ddl: set proper default flen of decimal(0) columns (#54028)

[ti-chi-bot]

This is an automated cherry-pick of #54028

What problem does this PR solve?

Issue Number: close #53779

Problem Summary:

See #53779.

What changed and how does it work?

Handle Decimal(0) properly in preprocessing.

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (release-7.1@a0fdddb). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.1     #56893   +/-   ##
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  Coverage               ?   73.6726%           
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  Hits                   ?     282242           
  Misses                 ?      82960           
  Partials               ?      17901           

[tangenta]

/hold

[tangenta]

/unhold

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: tangenta, wjhuang2016

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• OWNERS [tangenta,wjhuang2016]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-11-12 04:06:45.146024945 +0000 UTC m=+329167.336893942: ☑️ agreed by tangenta.
• 2024-11-12 04:18:12.88553984 +0000 UTC m=+329855.076408853: ☑️ agreed by wjhuang2016.