Datenbanken & Informationssysteme

import DriveAsset from ’../../../../components/DriveAsset.astro’;

🗂️ Course Assets (Google Drive)

📐 Relational Algebra Fundamentals

The foundational operators in relational algebra:

Operator	Symbol	Meaning	Example
Selection	$\sigma_\varphi(R)$	Rows satisfying predicate $\varphi$	$\sigma_{\text{credits} \ge 6}(\text{Course})$
Projection	$\pi_{A_1, \dots, A_k}(R)$	Select specific columns	$\pi_{\text{name, matnr}}(\text{Student})$
Natural Join	$R \bowtie S$	Join on matching attribute names	$\text{Student} \bowtie \text{Enrollment}$
Theta Join	$R \bowtie_\theta S$	General condition join	$R \bowtie_{R.A < S.B} S$
Rename	$\rho_{S}(R)$	Renames relation or attributes	$\rho_{\text{Alumni}}(\text{Graduates})$

Example Query

Retrieve all students enrolled in “Datenbanken” with a grade $\le 2.0$ :

\pi_{\text{name, matnr}}\left( \sigma_{\text{title} = \text{'Datenbanken'} \land \text{grade} \le 2.0} (\text{Student} \bowtie \text{Exam} \bowtie \text{Course}) \right)

💻 Dockerized Lab Setup

# docker-compose.yml for local database lab
version: '3.8'

services:
  postgres-db:
    image: postgres:16-alpine
    container_name: uni_postgres
    restart: always
    environment:
      POSTGRES_USER: uni_user
      POSTGRES_PASSWORD: secretpassword
      POSTGRES_DB: university_vault
    ports:
      - "5432:5432"
    volumes:
      - pgdata:/var/lib/postgresql/data

volumes:
  pgdata: