Relational DBMS and SQL Execution Engine

An educational Relational Database Management System (RDBMS) built from scratch in modern C++20 with an interactive desktop GUI powered by Qt 6.

The goal of this project is to explore database internals "under the hood": query tokenization, finite-state machine (FSM) syntax parsing, relational query execution planning, and disk snapshot persistence.

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Architecture Overview

The system is decoupled into modular layers:

• Input: SQL Query string
• Lexer and Parser: Zero-regex Finite-State Machine (FSM) tokenizer and parser (O(N) token scan) validating grammar rules and syntax tokens
• Query Representation: Structured intermediate representation (Query command object) representing DDL, DML, or DQL commands
• Execution Engine: Evaluates relational queries, performing multi-condition filtering (WHERE), hash-based table joins (JOIN / LEFT JOIN), and hash-based aggregations (GROUP BY / HAVING)
• Storage Layer: Columnar in-memory table layout (std::vector<Column>) with file-based snapshot persistence, PRIMARY KEY / FOREIGN KEY constraint validation, and schema type management (INTEGER, NVARCHAR2, DATE)
• Desktop UI: Qt 6 graphical interface featuring QSyntaxHighlighter, query tabs, and table grid visualization via QAbstractTableModel

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Key Features

• Custom SQL Engine:
  • DDL: CREATE TABLE (with PRIMARY KEY uniqueness and FOREIGN KEY REFERENCES referential integrity checks), DROP TABLE.
  • DML: INSERT INTO, UPDATE, DELETE (full table or filtered via WHERE).
  • DQL: SELECT ... FROM ... WHERE with multi-conditional filtering (AND, comparison operators).
  • Aggregations and Grouping: Hash-based GROUP BY, HAVING, and aggregate functions (COUNT, SUM, MIN, MAX).
  • Relationships: Hash-based JOIN and LEFT JOIN evaluation (O(N + M)) between tables.
• Desktop Database Explorer (Qt 6):
  • Custom code editor with real-time SQL syntax highlighting (QSyntaxHighlighter).
  • Tabular data visualization implemented via QAbstractTableModel.
  • Tabbed query workspace and interactive schema explorer.
• Robust Verification:
  • 100+ automated unit and integration tests using GoogleTest covering parser state transitions, relational joins, aggregations, key constraints, and execution benchmarks.

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Screenshot

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Tech Stack and Prerequisites

• Language: C++20 (GCC 11+, Clang 13+, or MSVC 2019+)
• GUI Framework: Qt 6.x (Core, Gui, Widgets)
• Build System: CMake 3.20+
• Third-Party Libraries:
  • fmtlib for modern string formatting
  • googletest for test automation

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Building and Running

1. Clone the repository

git clone https://github.com/arseniizar/DBMS-cpp.git
cd DBMS-cpp

2. Build via CMake

cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j

3. Run the Application

./build/DatabaseProject

4. Run Unit Tests (GoogleTest)

cd build && ctest --output-on-failure