Relational Databases

Database Overview

• A database is a collection of related data organized in a way that supports easily processing the data

• A Database Management System (DBMS) is software that provides the ability to create and manipulate a database

• Examples of DBMSs: MySQL, PostgreSQL, MongoDB, Microsoft SQL Server, SQLite

Relational Databases

• A relational database models data as relations

• A relation is organized as a table of columns and rows

• Each column is also called an attribute

• Each row is also called a record

• Each row includes a unique key to identify that row

Database Languages

• Data definition language: defines the data types and relationships among them

• Data manipulation language: performs operations such as inserting, updating, or deleting data.

• Query language: performs information retrieval

SQL

• The Structured Query Language (SQL) combines the roles of all database languages into a single language for relational databases

• SQL is a declarative programming language

• A declarative programming language describes what computation should be performed not how to compute it

Relational Database Normalization

• Normalization is a systematic approach to organizing relational database tables to eliminate data redundancy and data manipulation anomalies

• Types of anomalies:

  • Update Anomaly

  • Insertion Anomaly

  • Deletions Anomaly