In-Memory Relational Database & Query DSL

A functional, in-memory relational database engine and custom Query Domain-Specific Language (DSL) built entirely in Scala.

This project simulates core SQL-like operations using pure functional programming paradigms (immutability, higher-order functions, and algebraic data types). It allows for complex tabular data manipulation, multi-table database management, and advanced filtering logic.

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🚀 Core Features

Table Manipulation (Table.scala)

• Core relational algebra operations:
  • select
  • filter
  • insert
  • delete
  • update
• Advanced operations:
  • join (handles overlapping columns and data merging)
  • cartesianProduct
• Sorting capabilities
• Dynamic CSV parsing

Filter DSL (FilterCond.scala)

• Composable filtering system using Algebraic Data Types (ADTs)
• Supports:
  • Predicates (Field)
  • Logical operators (And, Or, Not, Equal)
  • Collection evaluators (Any, All)

Database Management (Database.scala)

• Manages collections of tables
• Supports:
  • insert (create table)
  • delete (drop table)
  • update operations
  • table selection

Complex Queries (Queries.scala)

• Demonstrates chaining operations:
  • filtering with compound conditions
  • selecting columns
  • sorting results
• Enables extracting meaningful insights from tabular data

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📁 Project Structure

• src/main/scala/ -- Core database engine and DSL implementation\
• src/test/scala/ -- Test suite:
  • TestDatabase
  • TestFilter
  • TestQueries
  • TestTable
• build.sbt -- Scala Build Tool configuration

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💻 Building and Testing

The project uses sbt (Scala Build Tool).

Run in terminal

# Start sbt shell
sbt

# Run tests
test

Or directly:

sbt test

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🧠 Technical Highlights

Purely Functional

• No mutable state (var)
• Uses immutable collections:
  • List
  • Map
• Relies on transformations:
  • map
  • flatMap
  • foldLeft

Safe Data Handling

• Extensive use of Option[T]
• Avoids runtime exceptions
• Handles missing or invalid data safely