πreal

A free and open source Relational Algebra interpreter for learning databases.

Pireal lets you create relations, write Relational Algebra queries, and see results instantly, no SQL, no setup, no noise. Built for students and teachers who want to understand how databases actually work under the hood.

The origin story

Pireal was born in 2015 out of necessity. Back then the standard tool for practicing Relational Algebra in university courses was WinRDBI, a Windows-only application. The problem: I've been a Linux user my whole life, and when I took my databases course I simply couldn't use it.

Instead of dual-booting into Windows like a normal person, I wrote Pireal. Ten years later it's still here, still cross-platform, and WinRDBI is still Windows-only.

What is this

Most database courses jump straight to SQL and skip the theory entirely. Pireal takes a step back and lets you work directly with Relational Algebra, the mathematical foundation that SQL is built on. Once this clicks, SQL clicks.

You write queries like:

young := select age < 30 (students);
names := project name (young);

Hit F5, see the results. That's it.

Features

All core RA operators: select, project, njoin, union, intersect, difference, product, outer joins
Symbol mode: write σ, π, ⋈ instead of keywords if you're feeling fancy (or your professor insists)
AST viewer: inspect the syntax tree Pireal builds when parsing your query, useful if you're also taking a compilers course
SQL generator: translates any RA query to equivalent SQL so you can compare both languages side by side
Custom themes: drop a JSON file in ~/.pireal/themes/ and it shows up automatically
Plain text .pdb database files, readable by humans and version control alike

Installation

Windows

Download the installer from the releases page and follow the steps. Next, next, finish.

Linux

Download the AppImage from the releases page:

chmod +x Pireal-x86_64.AppImage
./Pireal-x86_64.AppImage

From source

Requires Python 3.12+ and uv.

git clone https://github.com/centaurialpha/pireal
cd pireal
uv run pireal

Documentation

Full docs, operator reference, examples and a theme creation guide at centaurialpha.github.io/pireal.

Contributing

uv sync --group dev
uvx pre-commit install
uv run pytest

Bug reports, fixes, and feature ideas are welcome. Open an issue or send a PR.

License

GNU GPLv3. See COPYING.

Pireal

Install / Use

README