Major features:
- Full SQL JOIN support (INNER, LEFT, RIGHT, FULL OUTER, CROSS)
- Subqueries (IN, EXISTS, scalar)
- Set operations (UNION, INTERSECT, EXCEPT)
- DISTINCT clause
- Prepared statements with PREPARE/EXECUTE/DEALLOCATE
- EXPLAIN PLAN for query optimization
- B-tree index optimization in WHERE clauses

Production infrastructure:
- Connection pooling with RAII guards
- Health checks and Prometheus metrics
- MD5 and SCRAM-SHA-256 authentication
- Rate limiting with token bucket algorithm
- WAL crash recovery testing
- Comprehensive test suite

This release brings DriftDB to near SQL feature parity with major databases.