Mysql 5.7 Changes [Experimental]

[sm745052]

No description provided.

[gemini-code-assist]

Summary of Changes

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This pull request introduces experimental support for MySQL 5.7 by refactoring the collation order query and updating the Java dialect adapter. The changes focus on ensuring compatibility with older MySQL versions that lack modern window functions, while simultaneously improving the performance of the collation mapping process for all supported MySQL versions.

Highlights

• MySQL 5.7 Compatibility: Updated the collation order query to replace window functions (FIRST_VALUE, DENSE_RANK) with temporary tables and GROUP BY joins, ensuring compatibility with MySQL 5.7 while maintaining support for 8.0+.
• Performance Improvements: Optimized the collation order query by materializing codepoints into a temporary table, avoiding redundant cross-joins and improving execution efficiency.
• Codebase Refactoring: Updated the Java adapter to handle MySQL 5.7 specific behavior regarding PAD_ATTRIBUTE and introduced a MySqlVersion enum to manage version-specific logic.

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[codecov]

Codecov Report

❌ Patch coverage is 91.75824% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 52.66%. Comparing base (d871e1e) to head (2d74fd8).
⚠️ Report is 17 commits behind head on main.

Files with missing lines	Patch %	Lines
.../uniformsplitter/stringmapper/CollationMapper.java	91.87%	3 Missing and 10 partials ⚠️
...jdbc/uniformsplitter/UniformSplitterDBAdapter.java	75.00%	1 Missing ⚠️
...niformsplitter/stringmapper/CollationOrderRow.java	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##               main    #3695       +/-   ##
=============================================
+ Coverage     33.32%   52.66%   +19.34%     
- Complexity      481     6285     +5804     
=============================================
  Files           215     1065      +850     
  Lines         12862    64557    +51695     
  Branches       1262     7149     +5887     
=============================================
+ Hits           4286    33998    +29712     
- Misses         8236    28267    +20031     
- Partials        340     2292     +1952     

Components	Coverage Δ
spanner-templates	72.32% <91.75%> (∅)
spanner-import-export	68.64% <ø> (∅)
spanner-live-forward-migration	80.87% <ø> (∅)
spanner-live-reverse-replication	77.58% <ø> (∅)
spanner-bulk-migration	89.43% <91.75%> (∅)
gcs-spanner-dv	85.75% <ø> (∅)

Files with missing lines	Coverage Δ
...c/main/java/org/apache/beam/it/gcp/JDBCBaseIT.java	0.00% <ø> (ø)
...jdbc/dialectadapter/mysql/MysqlDialectAdapter.java	97.94% <100.00%> (ø)
...c/uniformsplitter/stringmapper/CollationIndex.java	97.26% <100.00%> (ø)
...jdbc/uniformsplitter/UniformSplitterDBAdapter.java	60.00% <75.00%> (ø)
...niformsplitter/stringmapper/CollationOrderRow.java	96.66% <87.50%> (ø)
.../uniformsplitter/stringmapper/CollationMapper.java	93.30% <91.87%> (ø)

... and 868 files with indirect coverage changes

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