A lightweight, web-based SQL engine built with Python and FastAPI. This project features a custom SQL parser and executor that allows users to run SQL queries against a JSON-based storage system through a modern web interface.

• Web Interface: Clean, dark-themed UI for writing and executing SQL queries.
• Custom SQL Engine: Includes a hand-written tokenizer, parser, and executor.
• JSON Storage: Data is persisted in JSON format, making it easy to inspect and manage.
• Multi-Query Support: Execute multiple SQL statements separated by semicolons.
• Real-time Results: View query results in an interactive table with execution timing.

online_sql/
├── main.py              # FastAPI application & API routes
├── requirements.txt     # Python dependencies
├── engine/              # Core SQL Engine logic
│   ├── tokenizer.py     # Lexical analysis
│   ├── parser.py        # Syntactic analysis (AST generation)
│   ├── executor.py      # Query execution logic
│   └── storage.py       # JSON-based data persistence
├── data/                # Database storage (JSON files)
│   └── default/         # Default database namespace
└── static/              # Frontend assets
    └── index.html       # Web interface

• Python 3.8+

1. Clone the repository:

   git clone <repository-url>
   cd online_sql

2. Install dependencies:

   pip install -r requirements.txt

3. Run the application:

   python main.py

4. Access the UI: Open your browser and navigate to http://localhost:8000

You can run standard SQL commands via the web interface:

CREATE TABLE users (id INT, name VARCHAR, email VARCHAR);

INSERT INTO users VALUES (1, 'John Doe', 'john@example.com');
INSERT INTO users VALUES (2, 'Jane Smith', 'jane@example.com');

SELECT * FROM users WHERE id = 1;

1. Tokenizer: Breaks the raw SQL string into a stream of tokens (keywords, identifiers, operators).
2. Parser: Analyzes the token stream to build an Abstract Syntax Tree (AST) based on SQL grammar.
3. Executor: Traverses the AST and performs the requested operations (Reading/Writing to JSON files in the data/ directory).
4. API: FastAPI handles the communication between the frontend and the engine.

MIT