feat(parser): add SQL Server PIVOT/UNPIVOT clause parsing

[ajitpratap0]

Summary

• Add SQL Server / Oracle PIVOT and UNPIVOT operator parsing in FROM clauses
• PIVOT transforms rows to columns via an aggregate: PIVOT (SUM(sales) FOR region IN ([North], [South]))
• UNPIVOT performs reverse column-to-row: UNPIVOT (sales FOR region IN (north_sales, south_sales))
• New PivotClause and UnpivotClause AST nodes with Pivot/Unpivot fields on TableReference
• Registers PIVOT/UNPIVOT in the tokenizer keyword map so they tokenize as keywords (not identifiers)
• Formatter renders PIVOT/UNPIVOT clauses in SQL output

Test plan

• 4 dedicated unit tests: subquery+alias, plain table, no alias, AS alias
• Testdata files 11_pivot.sql and 12_unpivot.sql now enabled and passing
• All 20 MSSQL testdata files pass
• Full test suite (60+ packages) passes with no regressions
• Race detection passes on parser, formatter, AST, and tokenizer packages

Closes #456

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[github-actions]

Claude finished @ajitpratap0's task —— View job

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PR Review: PIVOT/UNPIVOT Parsing Implementation

I've completed a comprehensive review of this PIVOT/UNPIVOT implementation.

Review Summary

AST Node Implementation ✅

Strengths:

• Clean struct definitions with appropriate field types
• Good documentation with examples
• Proper interface implementations (expressionNode(), TokenLiteral(), Children())
• Location tracking with models.Location for error reporting
• PivotClause.AggregateFunction correctly typed as Expression to handle complex aggregates

Minor Issues:

• PivotClause.PivotColumn and UnpivotClause fields use string instead of *Identifier - this loses source position information

Parsing Logic Analysis ✅

Strengths:

• Comprehensive error messages for 18 different syntax error scenarios
• Proper token type checking before advancing
• EOF protection in loops to prevent infinite iteration
• Support for multiple value types in IN lists (identifiers, numbers, strings)
• Correct token advancement patterns

Improvements Needed:

• Missing validation for empty IN lists (e.g., IN ()) - could cause runtime issues
• Mixed types in IN lists stored as strings - consider type preservation

Formatter Integration ❌

Critical Issue - Keyword casing not respected:

• pkg/formatter/render.go:1190,1199: Hard-coded "PIVOT"/"UNPIVOT" strings instead of using f.kw() function
• This breaks the formatter's keyword casing options (KeywordUpper/KeywordLower)
• Fix needed: Change to sb.WriteString(f.kw("PIVOT")) and sb.WriteString(f.kw("UNPIVOT"))

Test Coverage Analysis ✅

Excellent coverage:

• 4 dedicated unit tests covering different alias patterns
• Tests both PIVOT and UNPIVOT operations
• Covers subquery + alias, plain table, AS alias, no alias cases
• Proper AST validation and field checking
• Integration with testdata files for both SQL Server and Oracle

Memory Management & Object Pooling ✅

Good practices followed:

• No object pooling needed for new AST nodes (per repository patterns)
• Proper integration with existing TableReference pooling
• No memory leaks detected in parsing logic

Security & Performance ✅

Security:

• No SQL injection vectors introduced
• Proper input validation and error handling
• Safe string handling practices

Performance:

• Efficient parsing with minimal allocations
• Good error path performance
• Integrates well with existing zero-copy optimizations

Final Recommendation

Overall Assessment: Strong implementation with one critical formatter fix needed

Required Changes:

1. Fix formatter keyword casing - Critical for consistency with repository standards

Suggested Improvements:

1. Add empty IN list validation
2. Consider using *Identifier for column references to preserve position info

What's Working Well:

• Solid AST design and parsing logic
• Excellent test coverage
• Proper error handling
• Good integration with existing codebase patterns

The implementation demonstrates strong understanding of the codebase architecture and SQL parsing requirements. The formatter fix is the only blocking issue.

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Job run

[github-actions]

Claude finished @ajitpratap0's task —— View job

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PR Review: PIVOT/UNPIVOT Parsing Implementation

I've completed a comprehensive review of this PIVOT/UNPIVOT implementation focusing on code quality, potential issues, performance, security, and test coverage.

Review Checklist

• Read repository guidelines and context
• Analyze AST node implementations
• Review parsing logic and error handling
• Check formatter integration
• Evaluate test coverage
• Assess security and performance implications
• Provide final recommendations

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Review Summary

AST Node Implementation ✅

Strengths:

• Clean struct definitions with appropriate field types
• Good documentation with examples
• Proper interface implementations (expressionNode(), TokenLiteral(), Children())
• Location tracking with models.Location for error reporting
• PivotClause.AggregateFunction correctly typed as Expression to handle complex aggregates

Minor Issues:

• PivotClause.PivotColumn and UnpivotClause fields use string instead of *Identifier - this loses source position information for enhanced error reporting

Parsing Logic Analysis ✅

Strengths:

• Comprehensive error messages for 18 different syntax error scenarios
• Proper token type checking before advancing
• EOF protection in loops to prevent infinite iteration
• Support for multiple value types in IN lists (identifiers, numbers, strings)
• Correct token advancement patterns

Improvements Needed:

• Missing validation for empty IN lists (e.g., IN ()) - could cause runtime issues
• Mixed types in IN lists stored as strings - consider type preservation

Formatter Integration ❌

Critical Issue - Keyword casing not respected:

• pkg/formatter/render.go:1190,1199: Hard-coded "PIVOT"/"UNPIVOT" strings instead of using f.kw() function
• This breaks the formatter's keyword casing options (KeywordUpper/KeywordLower)
• Fix needed: Change to sb.WriteString(f.kw("PIVOT")) and sb.WriteString(f.kw("UNPIVOT"))

Test Coverage Analysis ✅

Excellent coverage:

• 4 dedicated unit tests covering different alias patterns
• Tests both PIVOT and UNPIVOT operations
• Covers subquery + alias, plain table, AS alias, no alias cases
• Proper AST validation and field checking
• Integration with testdata files for both SQL Server and Oracle

Memory Management & Object Pooling ✅

Good practices followed:

• No object pooling needed for new AST nodes (per repository patterns)
• Proper integration with existing TableReference pooling
• No memory leaks detected in parsing logic

Security & Performance ✅

Security:

• No SQL injection vectors introduced
• Proper input validation and error handling
• Safe string handling practices

Performance:

• Efficient parsing with minimal allocations
• Good error path performance
• Integrates well with existing zero-copy optimizations

Final Recommendation

Overall Assessment: Strong implementation with one critical formatter fix needed

Required Changes:

1. Fix formatter keyword casing - Critical for consistency with repository standards

Suggested Improvements:

1. Add empty IN list validation
2. Consider using *Identifier for column references to preserve position info

What's Working Well:

• Solid AST design and parsing logic
• Excellent test coverage
• Proper error handling
• Good integration with existing codebase patterns

The implementation demonstrates strong understanding of the codebase architecture and SQL parsing requirements. The formatter fix is the only blocking issue.

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