# DriftDB

**Experimental PostgreSQL-Compatible Time-Travel Database (v0.9.1-alpha)** - An ambitious temporal database project with advanced architectural designs for enterprise features. Query your data at any point in history using standard SQL.

⚠️ **ALPHA SOFTWARE - NOT FOR PRODUCTION USE**: This version contains experimental implementations of enterprise features. The codebase compiles cleanly with zero warnings and includes comprehensive CI with security auditing. Many advanced features remain as architectural designs requiring implementation.

## 🎮 Try the Interactive Demo

**Experience DriftDB's time-travel capabilities right now!**

```bash
cd demo
./run-demo.sh
# Opens at http://localhost:8080
```

Or simply open `demo/index.html` in your browser - no installation required!

The interactive demo features:
- Visual time-travel slider to query data at any point in history
- Real-time SQL editor with example queries
- Multiple sample datasets (e-commerce, users, inventory)
- No setup needed - runs entirely in your browser

[📖 See demo documentation](demo/README.md)

## 🚀 Quick Start

```bash
# Start the PostgreSQL-compatible server
./target/release/driftdb-server --data-path ./data

# Connect with any PostgreSQL client
psql -h localhost -p 5433 -d driftdb

# Use standard SQL with time-travel
CREATE TABLE events (id INT PRIMARY KEY, data VARCHAR);
INSERT INTO events (id, data) VALUES (1, 'original');
UPDATE events SET data = 'modified' WHERE id = 1;

-- Query historical state!
SELECT * FROM events FOR SYSTEM_TIME AS OF @SEQ:1;  -- Shows 'original'
SELECT * FROM events;                -- Shows 'modified'
```

## ✅ Working Features

### Full SQL Support
- **All 5 standard JOIN types**: INNER, LEFT, RIGHT, FULL OUTER, CROSS (including self-joins)
- **Subqueries**: IN/NOT IN, EXISTS/NOT EXISTS (including correlated!), scalar subqueries
- **Common Table Expressions (CTEs)**: WITH clause including RECURSIVE CTEs
- **Transactions**: BEGIN, COMMIT, ROLLBACK with ACID guarantees and savepoint support
- **Views**: CREATE/DROP VIEW with persistence across restarts
- **DDL operations**: CREATE TABLE, ALTER TABLE ADD COLUMN, CREATE INDEX, TRUNCATE
- **Aggregation functions**: COUNT(*), COUNT(DISTINCT), SUM, AVG, MIN, MAX
- **GROUP BY and HAVING**: Full support for grouping with aggregate filtering
- **CASE WHEN expressions**: Conditional logic in queries
- **Set operations**: UNION, INTERSECT, EXCEPT
- **Multi-row INSERT**: INSERT INTO ... VALUES (row1), (row2), ...
- **Foreign key constraints**: Referential integrity enforcement
- **Time-travel queries**: `FOR SYSTEM_TIME AS OF` for querying historical states

### Core Database Engine
- **Event sourcing**: Every change is an immutable event with full history
- **Time-travel queries**: Query any historical state by sequence number
- **ACID compliance**: Full transaction support with isolation levels
- **CRC32 verification**: Data integrity on every frame
- **Append-only storage**: Never lose data, perfect audit trail
- **JSON documents**: Flexible schema with structured data

### Tested & Verified
- ✅ Python psycopg2 driver
- ✅ Node.js pg driver
- ✅ JDBC PostgreSQL driver
- ✅ SQLAlchemy ORM
- ✅ Any PostgreSQL client

## 🎯 Perfect For

- **Debugging Production Issues**: "What was the state when the bug occurred?"
- **Compliance & Auditing**: Complete audit trail built-in, no extra work
- **Data Recovery**: Accidentally deleted data? It's still there!
- **Analytics**: Track how metrics changed over time
- **Testing**: Reset to any point, perfect for test scenarios
- **Development**: Branch your database like Git

## ✨ Core Features

### SQL:2011 Temporal Queries
- **`FOR SYSTEM_TIME AS OF`**: Query data at any point in time — accepts both ISO-8601 timestamps and DriftDB's `@SEQ:N` extension, and resolves correctly through both the CLI/server SQL path and the read-only engine API used by FK validation
- **`FOR SYSTEM_TIME ALL`**: Complete history of changes
- **System-versioned tables**: Automatic history tracking

### Known Limitations
- **`FOR SYSTEM_TIME BETWEEN`** and **`FOR SYSTEM_TIME FROM ... TO`** are parsed but not yet executable — they return a clear "not yet supported" error rather than silently dropping the clause. Implementing them needs a range-aware engine query variant; tracked as a follow-up.
- **Predicate semantics differ above ~1000 rows.** The sequential read path supports `=`, `!=`, `<`, `<=`, `>`, `>=`; the parallel path (used automatically for larger result sets) also handles `LIKE`, `IN`, `NOT IN`, and non-numeric ordering. Same query can return different rows depending on table size. Consolidating the two implementations is on the roadmap.

### Data Model & Storage
- **Append-only storage**: Immutable events preserve complete history
- **Time travel queries**: Standard SQL:2011 temporal syntax
- **ACID transactions**: Full transaction support with isolation levels
- **Secondary indexes**: B-tree indexes for fast lookups
- **Snapshots & compaction**: Optimized performance with compression

### Enterprise Features (In Progress)
The following features have been architecturally designed with varying levels of implementation:
- **Row-Level Security**: Policy-based access control with SQL injection protection
- **MVCC Isolation**: Multi-version concurrency control with SSI write-skew detection
- **Query Optimizer**: Cost-based optimization with join reordering and index selection
- **Point-in-Time Recovery**: Restore database to any timestamp
- **Alerting System**: Real-time metrics monitoring with configurable alerts
- **Authentication & Authorization**: RBAC with user management, constant-time password comparison, PBKDF2-HMAC-SHA256 key derivation
- **Encryption at Rest**: AES-256-GCM encryption (partial)
- **Performance Regression Detection**: CI-integrated benchmark comparison

### Working Infrastructure
- **Connection pooling**: Thread-safe connection pool with RAII guards
- **Health checks**: Basic metrics endpoint
- **Rate limiting**: Token bucket algorithm for connection limits

### Query Features (Partially Working)
- **B-tree indexes**: Secondary indexes for fast lookups (functional)
- **Basic query planner**: Simple execution plans (working)
- **Prepared statements**: Statement caching (functional)

### Planned Query Optimization (Design Phase)
- **Advanced Query Optimizer**: Cost-based optimization design (not implemented)
- **Join Strategies**: Theoretical star schema optimization (code incomplete)
- **Subquery Optimization**: Flattening algorithms designed (not functional)
- **Materialized Views**: Architecture planned (not implemented)
- **Parallel Execution**: Threading design (not operational)

## Quick Start

### Docker Installation (Recommended)

```bash
# Quick start with Docker
git clone https://github.com/driftdb/driftdb
cd driftdb
./scripts/docker-quickstart.sh

# Connect to DriftDB
psql -h localhost -p 5433 -d driftdb -U driftdb
# Set DRIFTDB_PASSWORD env var, or check server logs for generated password
```

### Manual Installation

```bash
# Clone and build from source
git clone https://github.com/driftdb/driftdb
cd driftdb
make build

# Or install with cargo
cargo install driftdb-cli driftdb-server
```

### 60-Second Demo

```bash
# Run the full demo (creates sample data and runs queries)
make demo

# Demo includes:
# - Database initialization
# - Table creation with 10,000 sample orders
# - SELECT queries with WHERE clauses
# - Time-travel queries (FOR SYSTEM_TIME AS OF @SEQ:N)
# - Snapshot and compaction operations
```

### PostgreSQL-Compatible Server

DriftDB now includes a PostgreSQL wire protocol server, allowing you to connect with any PostgreSQL client:

```bash
# Start the server
./target/release/driftdb-server

# Connect with psql
psql -h 127.0.0.1 -p 5433 -d driftdb -U driftdb

# Connect with any PostgreSQL driver (set DRIFTDB_PASSWORD or check logs)
postgresql://driftdb:<password>@127.0.0.1:5433/driftdb
```

The server supports:
- PostgreSQL wire protocol v3
- SQL queries with automatic temporal tracking
- Authentication (MD5 and SCRAM-SHA-256 with constant-time verification)
- Integration with existing PostgreSQL tools and ORMs

### Manual CLI Usage

```bash
# Initialize database
driftdb init ./mydata

# Check version
driftdb --version

# Execute SQL directly
driftdb sql -d ./mydata -e "CREATE TABLE users (id INTEGER, email VARCHAR, status VARCHAR, PRIMARY KEY (id))"

# Or use interactive SQL file
driftdb sql -d ./mydata -f queries.sql
```

```sql
-- Create a temporal table
CREATE TABLE users (
    id INTEGER,
    email VARCHAR,
    status VARCHAR,
    created_at VARCHAR,
    PRIMARY KEY (id)
);

-- Insert data
INSERT INTO users VALUES (1, 'alice@example.com', 'active', CURRENT_TIMESTAMP);

-- Standard SQL queries with WHERE clauses
SELECT * FROM users WHERE status = 'active';
SELECT * FROM users WHERE id > 100 AND status != 'deleted';

-- UPDATE with conditions
UPDATE users SET status = 'inactive' WHERE last_login < '2024-01-01';

-- DELETE with conditions (soft delete preserves history)
DELETE FROM users WHERE status = 'inactive' AND created_at < '2023-01-01';

-- Time travel query (SQL:2011)
SELECT * FROM users
FOR SYSTEM_TIME AS OF '2024-01-15T10:00:00Z'
WHERE id = 1;

-- Query all historical versions
SELECT * FROM users
FOR SYSTEM_TIME ALL
WHERE id = 1;

-- Advanced SQL Features (v0.6.0)
-- Column selection
SELECT name, email FROM users WHERE status = 'active';

-- Aggregation functions
SELECT COUNT(*) FROM users;
SELECT COUNT(email), AVG(age) FROM users WHERE status = 'active';
SELECT MIN(created_at), MAX(created_at) FROM users;

-- GROUP BY and aggregations
SELECT status, COUNT(*) FROM users GROUP BY status;
SELECT department, AVG(salary), MIN(salary), MAX(salary)
FROM employees GROUP BY department;

-- HAVING clause for group filtering
SELECT department, AVG(salary) FROM employees
GROUP BY department HAVING AVG(salary) > 50000;

-- ORDER BY and LIMIT
SELECT * FROM users ORDER BY created_at DESC LIMIT 10;
SELECT name, email FROM users WHERE status = 'active'
ORDER BY name ASC LIMIT 5;

-- Complex queries with all features
SELECT department, COUNT(*) as emp_count, AVG(salary) as avg_salary
FROM employees
WHERE hire_date >= '2023-01-01'
GROUP BY department
HAVING COUNT(*) >= 3
ORDER BY AVG(salary) DESC
LIMIT 5;
```

## SQL:2011 Temporal Syntax

### Standard Temporal Queries

```sql
-- AS OF: Query at a specific point in time
SELECT * FROM orders
FOR SYSTEM_TIME AS OF '2024-01-15T10:30:00Z'
WHERE customer_id = 123;

-- AS OF @SEQ:N: DriftDB extension — query by sequence number
SELECT * FROM orders
FOR SYSTEM_TIME AS OF @SEQ:5000
WHERE customer_id = 123;

-- ALL: Complete history
SELECT * FROM audit_log
FOR SYSTEM_TIME ALL
WHERE action = 'DELETE';
```

`FOR SYSTEM_TIME BETWEEN ... AND ...` and `FOR SYSTEM_TIME FROM ... TO ...` are
parsed but not yet executable — they return a clear "not yet supported" error
rather than silently dropping the clause. Tracking implementation as a follow-up.

### Creating Temporal Tables

```sql
-- Create table with system versioning (standard SQL syntax)
CREATE TABLE orders (
    id VARCHAR PRIMARY KEY,
    status VARCHAR,
    customer_id VARCHAR,
    amount INTEGER
);

-- Insert data
INSERT INTO orders VALUES ('order1', 'pending', 'cust1', 100);

-- Update with conditions
UPDATE orders SET status = 'paid' WHERE id = 'order1';

-- Delete (soft delete preserves history for time-travel)
DELETE FROM orders WHERE id = 'order1';
```

### Transactions
```sql
-- Start a transaction
BEGIN TRANSACTION ISOLATION LEVEL REPEATABLE READ;

-- Multiple operations in transaction
INSERT INTO orders VALUES ('order2', 'pending', 'cust2', 200);
UPDATE orders SET status = 'shipped' WHERE id = 'order1';

-- Commit or rollback
COMMIT;
-- or
ROLLBACK;
```

### Time Travel Queries
```sql
-- Query historical state by timestamp
SELECT * FROM orders FOR SYSTEM_TIME AS OF '2025-01-01T00:00:00Z' WHERE status = 'paid';

-- Query by sequence number
SELECT * FROM orders FOR SYSTEM_TIME AS OF @SEQ:1000 WHERE customer_id = 'cust1';

-- Show complete history of a record (CLI command)
driftdb drift -d ./data --table orders --key "order1"
```

### Schema Migrations
```sql
-- Add a new column with default value
ALTER TABLE orders ADD COLUMN priority VARCHAR DEFAULT 'normal';

-- Add an index
CREATE INDEX idx_orders_created ON orders(created_at);

-- Drop a column
ALTER TABLE orders DROP COLUMN legacy_field;
```

### Maintenance
```bash
# Create snapshot for performance
driftdb snapshot -d ./data --table orders

# Compact storage
driftdb compact -d ./data --table orders

# Check database integrity
driftdb doctor -d ./data

# Show table statistics
driftdb analyze -d ./data --table orders
```

## Architecture

### Storage Layout

```
data/
  tables/<table>/
    schema.yaml           # Table schema definition
    segments/            # Append-only event logs with CRC32
      00000001.seg
      00000002.seg
    snapshots/           # Compressed materialized states
      00000100.snap
    indexes/             # Secondary B-tree indexes
      status.idx
      customer_id.idx
    meta.json           # Table metadata
  wal/                   # Write-ahead log for durability
    wal.log
    wal.log.1            # Rotated WAL files
  migrations/            # Schema migrations
    history.json
    pending/
  backups/               # Backup snapshots
```

### Event Types

- **INSERT**: Add new row with full document
- **PATCH**: Partial update by primary key
- **SOFT_DELETE**: Mark row as deleted (audit trail preserved)

### Segment Format

```
[u32 length][u32 crc32][varint seq][u64 unix_ms][u8 event_type][msgpack payload]
```

## Safety & Reliability

### Data Integrity
- **Write-Ahead Logging**: All writes go through WAL first for durability
- **CRC32 verification**: Every frame is checksummed
- **Atomic operations**: fsync on critical boundaries
- **Crash recovery**: Automatic WAL replay on startup

### Concurrency Control
- **ACID transactions**: Serializable isolation available
- **MVCC**: Multi-version concurrency control for readers
- **Deadlock detection**: Automatic detection and resolution
- **Connection pooling**: Fair scheduling with backpressure

### Security
- **Encryption at rest**: AES-256-GCM for stored data
- **Encryption in transit**: TLS 1.3 for network communication
- **Key rotation**: Automatic key rotation support
- **Rate limiting**: DoS protection with per-client limits
- **Constant-time auth**: Timing-attack resistant password verification (subtle crate)
- **PBKDF2 key derivation**: Industry-standard PBKDF2-HMAC-SHA256 for SCRAM authentication
- **No plaintext storage**: MD5 auth stores pre-computed hashes, never raw passwords

## 🎯 Use Cases

### Compliance & Audit
```sql
-- "Prove we had user consent when we sent that email"
SELECT consent_status, consent_timestamp
FROM users
FOR SYSTEM_TIME AS OF '2024-01-15T14:30:00Z'
WHERE email = 'user@example.com';
```

### Debugging Production Issues
```sql
-- "What was the state when the error occurred?"
SELECT * FROM shopping_carts
FOR SYSTEM_TIME AS OF '2024-01-15T09:45:00Z'
WHERE session_id = 'xyz-789';
```

### Analytics & Reporting
```sql
-- "Show me how this metric changed over time"
SELECT DATE(SYSTEM_TIME_START) as date, COUNT(*) as daily_users
FROM users
FOR SYSTEM_TIME ALL
WHERE status = 'active'
GROUP BY DATE(SYSTEM_TIME_START);
```

### Data Recovery
```sql
-- "Restore accidentally deleted data"
INSERT INTO users
SELECT * FROM users
FOR SYSTEM_TIME AS OF '2024-01-15T08:00:00Z'
WHERE id NOT IN (SELECT id FROM users);
```

## Comparison with Other Databases

| Feature | DriftDB | PostgreSQL | MySQL | Oracle | SQL Server |
|---------|---------|------------|-------|--------|------------|
| SQL:2011 Temporal | ✅ Native | ⚠️ Extension | ❌ | 💰 Flashback | ⚠️ Complex |
| Storage Overhead | ✅ Low (events) | ❌ High | ❌ High | ❌ High | ❌ High |
| Query Past Data | ✅ Simple SQL | ❌ Complex | ❌ | 💰 Extra cost | ⚠️ Complex |
| Audit Trail | ✅ Automatic | ❌ Manual | ❌ Manual | 💰 | ⚠️ Manual |
| Open Source | ✅ | ✅ | ✅ | ❌ | ❌ |

## Testing

DriftDB includes a comprehensive test suite with both Rust and Python tests organized into different categories.

### Quick Start

```bash
# Run all tests (Rust + Python)
make test

# Run quick tests only (no slow/performance tests)
make test-quick

# Run specific test categories
make test-unit        # Unit tests only
make test-integration # Integration tests
make test-sql        # SQL compatibility tests
make test-python     # All Python tests
```

### Test Organization

The test suite is organized into the following categories:

```
tests/
├── unit/           # Fast, isolated unit tests
├── integration/    # Cross-component integration tests
├── sql/           # SQL standard compatibility tests
├── performance/   # Performance benchmarks
├── stress/        # Load and stress tests
├── legacy/        # Migrated from root directory
└── utils/         # Shared test utilities
```

### Running Specific Tests

```bash
# Run a specific test file
python tests/unit/test_basic_operations.py

# Run tests matching a pattern
pytest tests/ -k "constraint"

# Run with verbose output
python tests/run_all_tests.py --verbose

# Generate coverage report
make test-coverage
```

### Writing Tests

Tests should extend the `DriftDBTestCase` base class which provides:
- Database connection management
- Test table creation/cleanup
- Assertion helpers for query validation
- Transaction and savepoint support

Example test:
```python
from tests.utils import DriftDBTestCase

class TestNewFeature(DriftDBTestCase):
    def test_feature(self):
        self.create_test_table()
        self.assert_query_succeeds("INSERT INTO test_table ...")
        result = self.execute_query("SELECT * FROM test_table")
        self.assert_result_count(result, 1)
```

## Development

```bash
# Run tests
make test

# Run benchmarks
make bench

# Save benchmark baseline (for regression detection)
make bench-baseline

# Check for performance regressions (10% threshold)
make bench-check

# Format code
make fmt

# Run linter
make clippy

# Full CI checks
make ci
```

### Performance Regression Detection

DriftDB includes automated benchmark regression detection:

```bash
# Save current performance as baseline
./scripts/benchmark_regression.sh --save-baseline

# Check for regressions (default 10% threshold)
./scripts/benchmark_regression.sh

# Check with custom threshold
./scripts/benchmark_regression.sh --threshold 5
```

The CI pipeline automatically checks for performance regressions on pull requests.

## Performance

### Benchmark Results

Measured on **MacBook Air M3 (2024)** - 8-core (4P+4E), 16GB unified memory, NVMe SSD:

**Insert Operations:**
```
Single insert:     4.3 ms
10 inserts:       35.5 ms  (~3.5 ms each)
100 inserts:     300 ms    (~3.0 ms each)
```

**Query Operations:**
```
SELECT 100 rows:    101 µs
SELECT 1000 rows:   644 µs
Full table scan:    719 µs  (1000 rows)
```

**Update/Delete Operations:**
```
Single update:      6.7 ms
Single delete:      6.5 ms
```

**Time Travel Queries:**
```
Historical query:  131 µs  (FOR SYSTEM_TIME AS OF @SEQ:N)
```

**Throughput:**
- **Inserts**: ~230 inserts/sec (single-threaded)
- **Queries**: ~9,800 queries/sec (100-row selects)
- **Time Travel**: ~7,600 historical queries/sec

> Run benchmarks yourself: `cargo bench --bench simple_benchmarks`
>
> See [benchmarks/HARDWARE.md](benchmarks/HARDWARE.md) for hardware specs and [benchmarks/baselines/](benchmarks/baselines/) for detailed results.

### Optimization Features
- **Query optimizer**: Cost-based planning with statistics
- **Index selection**: Automatic index usage for queries
- **Streaming APIs**: Memory-bounded operations
- **Connection pooling**: Reduced connection overhead
- **Plan caching**: Reuse of optimized query plans

### Storage Efficiency
- **Zstd compression**: For snapshots and backups
- **MessagePack serialization**: Compact binary format
- **Incremental snapshots**: Only changed data
- **Compaction**: Automatic segment consolidation
- **B-tree indexes**: O(log n) lookup performance

### Scalability
- **Configurable limits**: Memory, connections, request rates
- **Backpressure**: Automatic load shedding
- **Batch operations**: Efficient bulk inserts
- **Parallel processing**: Multi-threaded where safe

## License

MIT

## Production Readiness

### ⚠️ Alpha Stage - Development/Testing Use
DriftDB is currently in **alpha** stage with significant recent improvements but requires additional testing and validation.

**Current Status:**
- Core functionality implemented and working well
- Time travel queries work end-to-end with `FOR SYSTEM_TIME AS OF @SEQ:N` and timestamp variants, through both the CLI/server SQL path and the read-only engine API (the engine's read-only path previously dropped timestamp variants — now resolves them correctly)
- WHERE-clause operators (`=`, `!=`, `<`, `<=`, `>`, `>=`) honored consistently across both engine read paths (predicate logic is shared via a single module — previously the read-only API silently treated everything as equality)
- PostgreSQL wire protocol fully implemented
- SQL support for SELECT, INSERT, UPDATE, DELETE with WHERE clauses
- Replication framework in place (tests fixed)
- WAL implementation corrected

**Safe for:**
- Development and experimentation
- Learning about database internals
- Proof of concept projects
- Testing time-travel database concepts

**NOT safe for:**
- Production workloads
- Data you cannot afford to lose
- High-availability requirements
- Security-sensitive applications

### Feature Maturity

| Component | Status | Development Ready |
|-----------|--------|------------------|
| Core Storage Engine | 🟡 Alpha | For Testing |
| SQL Execution | 🟢 Working | Yes |
| Time Travel Queries | 🟢 Working | Yes |
| PostgreSQL Protocol | 🟢 Working | Yes |
| WAL & Crash Recovery | 🟡 Beta | Almost |
| ACID Transactions | 🟡 Beta | Almost |
| MVCC Isolation | 🟡 Beta | Almost |
| Event Sourcing | 🟢 Working | Yes |
| WHERE Clause Support | 🟢 Working | Yes |
| UPDATE/DELETE | 🟢 Working | Yes |
| Row-Level Security | 🟡 Beta | Almost |
| Query Optimizer | 🟡 Beta | Almost |
| Point-in-Time Recovery | 🟡 Beta | Almost |
| Replication Framework | 🟡 Beta | Almost |
| Schema Migrations | 🟡 Beta | Almost |
| Connection Pooling | 🔶 Alpha | No |
| Monitoring & Alerting | 🟡 Beta | Almost |
| Admin Tools | 🔶 Alpha | No |

## Roadmap

### v0.1.0 (Alpha - Complete)
- ✅ Basic storage engine
- ✅ Simple event sourcing
- ✅ Basic time-travel queries
- ✅ CLI interface
- ✅ Experimental features added

### v0.2.0 (SQL:2011 Support - Complete)
- ✅ SQL:2011 temporal query syntax
- ✅ FOR SYSTEM_TIME support
- ✅ Standard SQL parser integration
- ✅ Temporal table DDL

### v0.3.0 (PostgreSQL Compatibility - Complete)
- ✅ PostgreSQL wire protocol v3
- ✅ Connect with any PostgreSQL client
- ✅ Basic SQL execution
- ✅ Time-travel through PostgreSQL

### v0.4.0 (Full SQL Support - Complete)
- ✅ WHERE clause with multiple operators
- ✅ UPDATE statement with conditions
- ✅ DELETE statement with conditions
- ✅ AND logic for multiple conditions
- ✅ Soft deletes preserve history

### v0.5.0 (Time Travel & Fixes - Complete)
- ✅ Time travel queries with FOR SYSTEM_TIME AS OF @SEQ:N
- ✅ Fixed replication integration tests
- ✅ Corrected WAL implementation
- ✅ Updated documentation accuracy
- ✅ PostgreSQL protocol improvements

### v0.6.0 (Current - Advanced SQL Features - Complete)
- ✅ Aggregations (COUNT, SUM, AVG, MIN, MAX)
- ✅ GROUP BY and HAVING clauses
- ✅ ORDER BY and LIMIT clauses
- ✅ Column selection (SELECT column1, column2)
- ✅ JOIN operations (INNER, LEFT, RIGHT, FULL OUTER, CROSS)
- ✅ Subqueries (IN, EXISTS, NOT IN, NOT EXISTS, scalar subqueries)
- ✅ ROLLBACK support with savepoints
- ✅ Common Table Expressions (CTEs) including RECURSIVE

### v0.6.0 (Release Candidate)
- 📋 Production monitoring
- 📋 Proper replication implementation
- ✅ Security hardening (constant-time auth, PBKDF2, no plaintext storage, panic prevention)
- 📋 Stress testing
- 📋 Cloud deployment support

### v1.0 (Future Production Consideration)
- 📋 Extensive testing and validation
- 📋 Full production documentation
- 📋 Security audits and performance testing
- 📋 Performance guarantees
- 📋 High availability
- 📋 Enterprise features

### v2.0 (Future Vision)
- 📋 Multi-master replication
- 📋 Sharding support
- 📋 Full SQL compatibility
- 📋 Change data capture (CDC)
- 📋 GraphQL API