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

[tangenta]

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

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-06-14 07:42:43.840971606 +0000 UTC m=+709717.894283531: ☑️ agreed by wjhuang2016.
• 2024-06-14 07:48:52.222478964 +0000 UTC m=+710086.275790886: ☑️ agreed by hawkingrei.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 55.7692%. Comparing base (b96a775) to head (1493036).
Report is 1038 commits behind head on master.

Additional details and impacted files

@@                Coverage Diff                @@
##             master     #54028         +/-   ##
=================================================
- Coverage   72.5347%   55.7692%   -16.7655%     
=================================================
  Files          1508       1628        +120     
  Lines        432015     602660     +170645     
=================================================
+ Hits         313361     336099      +22738     
- Misses        99268     243377     +144109     
- Partials      19386      23184       +3798     

Flag	Coverage Δ
integration	37.2117% <55.5555%> (?)
unit	71.4174% <88.8888%> (-0.1102%)	⬇️

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

Components	Coverage Δ
dumpling	52.8522% <ø> (-0.0945%)	⬇️
parser	∅ <ø> (∅)
br	50.6163% <ø> (+8.3535%)	⬆️

[GMHDBJD]

/run-cherrypick

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #54619.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #55068.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #55695.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #56893.