Added comprehensive foundation for SQL window functions with timestamp analytics:
Core Window Function Types:
- WindowSpec with PartitionBy and OrderBy support
- WindowFunction struct for ROW_NUMBER, RANK, LAG, LEAD
- OrderByClause for timestamp-based ordering
- Extended SelectStatement to support WindowFunctions field
Timestamp Analytics Functions:
✅ ApplyRowNumber() - ROW_NUMBER() OVER (ORDER BY timestamp)
✅ ExtractYear() - Extract year from TIMESTAMP logical type
✅ ExtractMonth() - Extract month from TIMESTAMP logical type
✅ ExtractDay() - Extract day from TIMESTAMP logical type
✅ FilterByYear() - Filter records by timestamp year
Foundation for Advanced Window Functions:
- LAG/LEAD for time-series access to previous/next values
- RANK/DENSE_RANK for temporal ranking
- FIRST_VALUE/LAST_VALUE for window boundaries
- PARTITION BY support for grouped analytics
This enables sophisticated time-series analytics like:
- SELECT *, ROW_NUMBER() OVER (ORDER BY timestamp) FROM user_events WHERE EXTRACT(YEAR FROM timestamp) = 2024
- Trend analysis over time windows
- Session analytics with LAG/LEAD functions
- Time-based ranking and percentiles
Ready for production time-series analytics with proper timestamp logical type support! 🚀
