# Release v0.6.7 - Query Optimization & Demo Database

**Release Date:** January 2025

This release introduces smart query pagination, large result estimation, and a comprehensive demo employees database with showcase SQL queries to help users learn and explore LibreDB Studio.

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## Highlights

- **Smart Query Pagination:** Automatic result limiting with silent handling and load-more functionality
- **Large Result Estimation:** Pre-execution row count estimation and user confirmation for unlimited queries
- **Component Refactoring:** Renamed Dashboard component to Studio for better clarity
- **Demo Employees Database:** Complete HR database schema with 100+ showcase SQL queries
- **Enhanced Showcase Queries:** Difficulty levels and fun intro messages for better learning experience

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## New Features

### Query Pagination System

Automatic pagination for SELECT queries to prevent browser freezes when dealing with large datasets.

**Key Features:**
- **Default Limit:** 500 rows per page (configurable via `DEFAULT_QUERY_LIMIT`)
- **Silent Auto-Limiting:** No interruption dialogs, results are automatically limited
- **Load More:** Users can load additional pages incrementally
- **Preserves User Limits:** Existing `LIMIT` clauses in queries are respected
- **Maximum Safe Limit:** 100,000 rows for "Load All" operations

**How It Works:**
1. User executes a SELECT query without a LIMIT clause
2. System automatically adds `LIMIT 500 OFFSET 0`
3. Results display with pagination metadata
4. "Load More" button appears when more rows are available

### Large Result Estimation

Pre-execution row count estimation for queries without LIMIT clauses to help users understand query impact.

**Features:**
- **Row Count Estimation:** Uses `EXPLAIN` or `COUNT(*)` to estimate result size
- **User Confirmation:** Optional confirmation dialog for potentially large result sets
- **Silent Limiting:** Alternative mode that silently limits without confirmation
- **Performance Insight:** Shows estimated execution impact before running query

**Implementation:**
- PostgreSQL: Uses `EXPLAIN` with `ANALYZE` for accurate estimates
- MySQL: Uses `EXPLAIN` and `COUNT(*)` subquery
- SQLite: Uses `EXPLAIN QUERY PLAN` with row count hints
- MongoDB: Uses `countDocuments()` before executing find queries

### Demo Employees Database

A comprehensive HR database schema designed for learning and demonstration purposes.

**Database Schema:**
- **employees** - Employee master data with personal information
- **departments** - Department hierarchy and management
- **positions** - Job positions and salary ranges
- **employee_departments** - Employee-department assignments (many-to-many)
- **salaries** - Salary history tracking
- **projects** - Project management
- **project_assignments** - Employee-project assignments
- **attendance** - Time tracking and attendance records

**Features:**
- Realistic data relationships and constraints
- Foreign keys and indexes for proper normalization
- Sample data for immediate query testing
- Compatible with PostgreSQL, MySQL, and SQLite

### Showcase SQL Queries

100+ curated SQL queries organized by difficulty level to help users learn SQL and explore the demo database.

**Organization:**
- **Difficulty Levels:** Beginner, Intermediate, Advanced, Expert
- **Categories:** Basic SELECT, JOINs, Aggregations, Window Functions, CTEs, Subqueries
- **Fun Intros:** Random intro messages with divider lines for engaging learning experience
- **Progressive Learning:** Queries build upon each other from simple to complex

**Query Categories:**
1. Basic SELECT and Filtering
2. JOINs (INNER, LEFT, RIGHT, FULL)
3. Aggregations and GROUP BY
4. Window Functions (RANK, ROW_NUMBER, PARTITION BY)
5. Common Table Expressions (CTEs)
6. Subqueries and Correlated Subqueries
7. Date Functions and Time Series Analysis
8. Advanced Analytics and Reporting

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## Architecture Changes

### Component Renaming

**Dashboard → Studio**

The main application component has been renamed from `Dashboard` to `Studio` to better reflect its purpose as a comprehensive database development studio.

**Impact:**
- Component file: `src/components/Dashboard.tsx` → `src/components/Studio.tsx`
- All internal references updated
- No API or external interface changes
- Backward compatible (no breaking changes)

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## Documentation

### Query Optimization Guide

New comprehensive documentation for query optimization features:

**Location:** `docs/QUERY_OPTIMIZATION.md`

**Sections:**
- Query Pagination System architecture
- Silent Auto-Limiting philosophy and implementation
- Load More functionality details
- Query EXPLAIN integration
- Performance insights and metrics
- Provider-specific optimizations

### Demo Database Documentation

Complete documentation for the demo employees database:

**Location:** `docs/postgres/demo-employee-database.md`

**Contents:**
- Complete schema documentation
- ER diagram and relationships
- Sample queries organized by category
- Learning paths and tutorials
- Performance considerations

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## Breaking Changes

None. All existing APIs remain compatible.

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## Bug Fixes

- Fixed query execution performance for large datasets
- Improved memory handling for unlimited query results
- Enhanced error messages for query optimization features

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## Dependencies

No new dependencies added in this release.

### Existing Dependencies
All existing database drivers and UI libraries remain unchanged:
- `pg` - PostgreSQL driver
- `mysql2` - MySQL driver
- `better-sqlite3` - SQLite driver (dynamic import)
- `mongodb` - MongoDB driver

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## Migration Guide

### For Users

No migration required. All existing connections and queries continue to work as before.

**New Behavior:**
- Queries without LIMIT clauses now automatically paginate to 500 rows
- Use "Load More" button to retrieve additional pages
- Large result estimation may show confirmation dialogs (if enabled)

### For Developers

If you have custom code referencing the Dashboard component:

```typescript
// Before (v0.6.6 and earlier)
import Dashboard from '@/components/Dashboard';

// After (v0.6.7)
import Studio from '@/components/Studio';
```

**Note:** The component API remains the same, only the name changed.

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## What's Next

### v0.7.0 (Planned)
- Query result export formats (CSV, JSON, Excel)
- Query history and saved queries management
- Query performance comparison tools
- Advanced query builder UI
- Real-time query execution monitoring

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## Contributors

- Query pagination and optimization features
- Large result estimation implementation
- Demo employees database schema design
- Showcase queries curation and documentation
- Component refactoring (Dashboard → Studio)

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## Full Changelog

### Added
- Query pagination system with automatic LIMIT handling
- Large result estimation with pre-execution row counting
- User confirmation dialogs for potentially large queries
- Silent auto-limiting mode for seamless workflow
- "Load More" functionality for incremental result loading
- Demo employees database schema (7 tables)
- 100+ showcase SQL queries with difficulty levels
- Random intro messages with divider lines for showcase queries
- `docs/QUERY_OPTIMIZATION.md` comprehensive guide
- `docs/postgres/demo-employee-database.md` demo database documentation

### Changed
- Renamed `Dashboard` component to `Studio` throughout codebase
- Enhanced query execution flow with pagination support
- Improved query result handling for large datasets
- Updated showcase query system with difficulty categorization
- Refined user experience for unlimited query handling

### Fixed
- Query performance issues with large result sets
- Memory management for unlimited queries
- Error handling in query optimization features

### Removed
- None

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## Screenshots

### Query Pagination
Automatic pagination controls appear when query results exceed the default limit, with "Load More" button for incremental loading.

### Large Result Estimation
Pre-execution estimation dialog showing estimated row count and execution impact before running potentially expensive queries.

### Demo Database Schema
Complete HR database schema with employees, departments, positions, salaries, projects, and attendance tables with proper relationships.

### Showcase Queries
Curated SQL queries organized by difficulty level with fun intro messages to enhance learning experience.

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## Performance Improvements

- **Query Execution:** Faster initial response time with automatic pagination
- **Memory Usage:** Reduced memory footprint for large result sets
- **Browser Stability:** Prevented browser freezes on unlimited queries
- **User Experience:** Seamless workflow with silent auto-limiting

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## Security

No security-related changes in this release.

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## Testing

All features have been tested with:
- PostgreSQL 12+ databases
- MySQL 8.0+ databases
- SQLite 3.x databases
- MongoDB 6.0+ databases
- Various query sizes (small to very large datasets)

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**Full Changelog:** [Compare v0.6.6...v0.6.7](https://github.com/libredb/libredb-studio/compare/v0.6.6...v0.6.7)

