LiteSQL

A lightweight SQL engine supporting in-memory table storage, basic SQL parsing, and query execution using a custom AST and planner. Designed with modular components inspired by real DBMS internals.

Features

• In-memory table storage

• Basic SQL parsing and execution

• Supports common SQL operations:

• CREATE TABLE table_name (...)

• INSERT INTO table_name VALUES (...)

• SELECT * FROM table_name

• Simple WHERE clauses with comparison operators

Setup and Installation

1. Clone the repository
2. Install required dependencies: pip install lark-parser
3. Run the interactive SQL shell: python main.py

Usage Examples

Start the LiteSQL shell:

$ python main.py
Welcome to LiteSQL! Type 'help' or '?' for help, 'exit' to quit.
litesql>

Create a table:

litesql> CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT, age INTEGER);
Table 'users' created with 3 columns

Insert data:

litesql> INSERT INTO users VALUES (1, 'John Doe', 30);
Inserted 1 row into 'users' (ID: 0)

Query data:

litesql> SELECT * FROM users;
id | name     | age
---+----------+----
1  | John Doe | 30
(1 rows)

Query with WHERE clause:

litesql> SELECT name FROM users WHERE age > 25;
name  

--------
John Doe
(1 rows)
Running Tests
python -m unittest tests/test_basic.py

Limitations

• Only supports basic SQL syntax
• In-memory storage only (no persistence)
• Limited data types (INTEGER, TEXT, FLOAT, DOUBLE)
• Simple WHERE conditions only (no complex expressions)
• No joins or aggregations yet

Future Enhancements

• Support for more SQL operations (UPDATE, DELETE)
• Expanded WHERE clause support
• Simple joins
• Basic aggregation functions (COUNT, SUM, AVG)
• File-based storage for persistence Transaction support