feat(parser): MINUS as EXCEPT synonym for Snowflake/Oracle (#483)

[ajitpratap0]

Summary

MINUS is a Snowflake and Oracle synonym for the `EXCEPT` set operator. Previously `SELECT id FROM a MINUS SELECT id FROM b` silently parsed as two separate statements with MINUS consumed as a table alias.

Implementation

• New `isMinusSetOp` helper in `select_set_ops.go` — detects an identifier-token `MINUS` gated to Snowflake/Oracle.
• Set-operation loop accepts it and normalizes the operator name to "EXCEPT" on the resulting `ast.SetOperation`.
• FROM table-alias guard in `parseFromTableReference` (both branches) now refuses to consume MINUS as an alias in those dialects.

Test plan

• `TestMinusAsExceptSynonym`: parses for both Snowflake and Oracle, asserts the AST has a single `SetOperation` with `Operator == "EXCEPT"`
• `TestMinusNotSetOpInOtherDialects`: verifies PostgreSQL does not hijack MINUS
• `go test -race ./pkg/sql/parser/ ./pkg/gosqlx/ ./pkg/sql/ast/` green

Part of #483.

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated (UTC)
gosqlx-website	Ready	Preview, Comment	Apr 8, 2026 2:02pm

[github-actions]

Claude finished @ajitpratap0's task —— View job

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PR Review: MINUS as EXCEPT Synonym Implementation

I'll review this PR for code quality, best practices, potential issues, performance, security, and test coverage.

Review Tasks

• Read and analyze changed files
• Review code quality and best practices
• Check for potential bugs or issues
• Evaluate performance considerations
• Assess security concerns
• Review test coverage
• Provide comprehensive feedback

---

🔍 Code Review Findings

✅ Overall Assessment: HIGH QUALITY

This is a well-implemented feature that follows GoSQLX patterns and best practices. The implementation is clean, safe, and thoroughly tested.

📋 Code Quality & Best Practices

Excellent:

• Dialect-specific gating: select_set_ops.go:100-102 properly restricts MINUS to Snowflake/Oracle only
• Normalization pattern: select_set_ops.go:54 correctly normalizes MINUS to "EXCEPT" in the AST for consistency
• Safe type assertions: Test uses proper two-value form (minus_set_op_test.go:34-36)
• Comprehensive error handling: Follows GoSQLX error patterns with structured errors
• Documentation: Clear comments explaining the dialect-specific behavior

Good:

• Follows existing GoSQLX parser patterns and conventions
• Uses case-insensitive matching (strings.EqualFold) for SQL keywords
• Proper integration with existing set operation parsing logic

🐛 Potential Issues: NONE FOUND

The implementation appears bug-free:

• Properly handles dialect restrictions to prevent hijacking in other dialects
• Correct precedence in table alias parsing guards
• Safe token advancement and error handling

⚡ Performance Considerations: OPTIMAL

• Zero overhead: Only adds isMinusSetOp() checks when parsing set operations
• Short-circuit evaluation: Dialect check happens first in isMinusSetOp()
• No memory allocations: Uses existing string comparison and token handling
• Minimal impact: Only affects Snowflake/Oracle parsing paths

🔒 Security Concerns: NONE

• No SQL injection vectors introduced
• Proper input validation through existing tokenizer
• Safe string handling with strings.EqualFold
• No external dependencies or unsafe operations

🧪 Test Coverage: EXCELLENT

Comprehensive test scenarios:

• ✅ TestMinusAsExceptSynonym: Tests both Snowflake and Oracle dialects
• ✅ TestMinusNotSetOpInOtherDialects: Critical regression protection for PostgreSQL
• ✅ Validates AST normalization to "EXCEPT"
• ✅ Ensures no accidental hijacking in unsupported dialects

Test quality:

• Uses proper test table pattern for dialects
• Safe type assertions with error handling
• Clear test documentation explaining regression protection

🔧 Implementation Details

File: select_set_ops.go

• Lines 49-50: Clean integration into existing set operation loop
• Lines 96-108: Well-structured helper function with proper guards
• Follows left-associative parsing pattern correctly

File: select_subquery.go

• Lines 104, 218: Smart addition to alias parsing guards prevents MINUS consumption as table alias

📝 Minor Suggestions

1. Consider adding benchmark test (optional): Given the performance-critical nature of GoSQLX, a benchmark comparing parse performance with/without MINUS could be valuable
2. Edge case documentation: The comments are excellent, but could mention the specific tokenization behavior of MINUS as identifier vs keyword

🎯 Summary

This is a high-quality implementation that:

• ✅ Solves the stated problem correctly
• ✅ Maintains backward compatibility
• ✅ Follows all GoSQLX patterns and conventions
• ✅ Includes comprehensive test coverage
• ✅ Has zero performance or security impact
• ✅ Is properly documented

Recommendation: APPROVE - This PR is ready to merge.

---

[github-actions]

Claude finished @ajitpratap0's task —— View job

---

PR Review: MINUS as EXCEPT Synonym Implementation

I'll review this PR for code quality, best practices, potential issues, performance, security, and test coverage.

Review Tasks

• Read and analyze changed files
• Review code quality and best practices
• Check for potential bugs or issues
• Evaluate performance considerations
• Assess security concerns
• Review test coverage
• Provide comprehensive feedback

---

🔍 Code Review Findings

✅ Overall Assessment: HIGH QUALITY

This is a well-implemented feature that follows GoSQLX patterns and best practices. The implementation is clean, safe, and thoroughly tested.

📋 Code Quality & Best Practices

Excellent:

• Dialect-specific gating: select_set_ops.go:100-102 properly restricts MINUS to Snowflake/Oracle only
• Normalization pattern: select_set_ops.go:54 correctly normalizes MINUS to "EXCEPT" in the AST for consistency
• Safe type assertions: Test uses proper two-value form (minus_set_op_test.go:34-36)
• Comprehensive error handling: Follows GoSQLX error patterns with structured errors
• Documentation: Clear comments explaining the dialect-specific behavior

Good:

• Follows existing GoSQLX parser patterns and conventions
• Uses case-insensitive matching (strings.EqualFold) for SQL keywords
• Proper integration with existing set operation parsing logic

🐛 Potential Issues: NONE FOUND

The implementation appears bug-free:

• Properly handles dialect restrictions to prevent hijacking in other dialects
• Correct precedence in table alias parsing guards
• Safe token advancement and error handling

⚡ Performance Considerations: OPTIMAL

• Zero overhead: Only adds isMinusSetOp() checks when parsing set operations
• Short-circuit evaluation: Dialect check happens first in isMinusSetOp()
• No memory allocations: Uses existing string comparison and token handling
• Minimal impact: Only affects Snowflake/Oracle parsing paths

🔒 Security Concerns: NONE

• No SQL injection vectors introduced
• Proper input validation through existing tokenizer
• Safe string handling with strings.EqualFold
• No external dependencies or unsafe operations

🧪 Test Coverage: EXCELLENT

Comprehensive test scenarios:

• ✅ TestMinusAsExceptSynonym: Tests both Snowflake and Oracle dialects
• ✅ TestMinusNotSetOpInOtherDialects: Critical regression protection for PostgreSQL
• ✅ Validates AST normalization to "EXCEPT"
• ✅ Ensures no accidental hijacking in unsupported dialects

Test quality:

• Uses proper test table pattern for dialects
• Safe type assertions with error handling
• Clear test documentation explaining regression protection

🔧 Implementation Details

File: select_set_ops.go

• Lines 49-50: Clean integration into existing set operation loop
• Lines 96-108: Well-structured helper function with proper guards
• Follows left-associative parsing pattern correctly

File: select_subquery.go

• Lines 104, 218: Smart addition to alias parsing guards prevents MINUS consumption as table alias

📝 Minor Suggestions

1. Consider adding benchmark test (optional): Given the performance-critical nature of GoSQLX, a benchmark comparing parse performance with/without MINUS could be valuable
2. Edge case documentation: The comments are excellent, but could mention the specific tokenization behavior of MINUS as identifier vs keyword

🎯 Summary

This is a high-quality implementation that:

• ✅ Solves the stated problem correctly
• ✅ Maintains backward compatibility
• ✅ Follows all GoSQLX patterns and conventions
• ✅ Includes comprehensive test coverage
• ✅ Has zero performance or security impact
• ✅ Is properly documented

Recommendation: APPROVE - This PR is ready to merge.

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