Improve DDL genereate method at migration prepare

[azexcy]

Revise #20207

Changes proposed in this pull request:

• Improve DDL generate.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 57 lines in your changes missing coverage. Please review.

Project coverage is 60.87%. Comparing base (ae4afbd) to head (2a17a36).
Report is 8645 commits behind head on master.

Files with missing lines	Patch %	Lines
.../core/metadata/generator/PipelineDDLGenerator.java	0.00%	17 Missing ⚠️
...eline/scenario/migration/MigrationJobPreparer.java	0.00%	15 Missing ⚠️
...prepare/datasource/AbstractDataSourcePreparer.java	0.00%	12 Missing ⚠️
...epare/datasource/PrepareTargetTablesParameter.java	0.00%	9 Missing ⚠️
...ql/prepare/datasource/MySQLDataSourcePreparer.java	0.00%	2 Missing ⚠️
...repare/datasource/OpenGaussDataSourcePreparer.java	0.00%	1 Missing ⚠️
...epare/datasource/PostgreSQLDataSourcePreparer.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #20245      +/-   ##
============================================
+ Coverage     60.86%   60.87%   +0.01%     
- Complexity     2421     2422       +1     
============================================
  Files          3873     3876       +3     
  Lines         54673    54690      +17     
  Branches       9306     9310       +4     
============================================
+ Hits          33275    33295      +20     
+ Misses        18545    18542       -3     
  Partials       2853     2853              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.