Description

The SQL parser was not properly unescaping\\ sequences in string literals, causingSELECT ASCII('\\') to fail or return incorrect results. This PR fixes the escape handling by usingString.fromCharCode(92) for proper backslash replacement and optimizes the parser for better performance by pre-compiling regex patterns.

SQL Standard Alignment: This PR improves alignment with common SQL database behavior. While backslash escaping (\\) is not part of core SQL-99, it's a widely supported extension in major databases (MySQL, PostgreSQL). The implementation correctly handles SQL-99's quote doubling ('') for escaping single quotes and adds functional backslash escaping as a common extension, making AlaSQL behave more consistently with PostgreSQL/MySQL.

Changes

Parser Grammar (src/alasqlparser.jison)

• Added pre-compiled regex patterns (reEscapedQuote,reDoubleQuote,reEscapedBackslash) in the parser initialization section to avoid creating regex objects on every parse operation (performance optimization)
• Updated STRING and NSTRING productions to use these pre-compiled patterns and handle\\ escape sequences
• Fixed backslash replacement to useString.fromCharCode(92) instead of string literal"\\" to ensure proper unescaping
• Regeneratedsrc/alasqlparser.js from updated grammar

Tests

• Createdtest/test489.js with comprehensive test coverage (8 test sections):
  • Basic backslash escaping ('\\' in SQL → single backslash character)
  • Multiple consecutive backslashes (1-5 backslashes tested)
  • Backslashes followed by doubled quotes in various combinations
  • Doubled quotes in various positions and patterns
  • Mixed backslash and quote combinations
  • Double-quoted strings behavior (documenting that double quotes are treated as literals, not escape sequences)
  • Parameterized queries with escaped data (round-trip testing through INSERT/SELECT)
  • Complex multi-character escape sequences
• Enabled previously commented backslash test intest/test376.js

The test suite systematically builds from simple to complex cases, ensuring robust coverage of all escape sequence combinations including static SQL strings and parameterized queries.

Example

// Now works correctlyalasql("VALUE OF SELECT ASCII('\\\\')");// Returns 92// Column names also reflect the unescaped valuealasql("SELECT ASCII('\\\\')");// Returns [{"ASCII('\\')": 92}]// String literals work as expected - proper unescapingalasql("VALUE OF SELECT '\\\\'");// Returns single backslash character (length 1)alasql("VALUE OF SELECT '\\\\\\\\'");// Returns two backslash characters (length 2)alasql("VALUE OF SELECT '\\\\\\\\\\\\'");// Returns three backslash characters (length 3)// Edge case: backslash followed by quotealasql("VALUE OF SELECT '\\\\'''");// Returns "\'" (backslash + quote)// Complex combinationsalasql("VALUE OF SELECT '\\\\''\\\\'''");// Returns "\\'\\" (backslash + quote + backslash + quote)// Parameterized queries preserve escaped charactersalasql("VALUE OF SELECT ?",["\\'"]);// Returns "\'" correctly

Performance

The regex patterns are now compiled once during parser initialization rather than being created on every parse operation, improving parser performance.

Checklist

• Tests added/updated
• All existing tests pass (1931+ passing)
• No security vulnerabilities introduced
• Performance optimized per code review feedback
• Edge cases tested and verified (multiple consecutive backslashes, escaped backslash + escaped quote)
• Backslash unescaping now works correctly using String.fromCharCode(92)
• Comprehensive test suite covering 1-5 backslashes, quote doubling, and complex combinations
• Double quote behavior documented (treated as literals in double-quoted strings)
• Parameterized query escaping tested (round-trip INSERT/SELECT validation)
• SQL-99 quote doubling compliance maintained, backslash escaping added as common extension

• FixesSELECT ASCII('\\') #489

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