Introdução a Bancos de Dados Relacionais e SQL

Introduction

A database is a structured set of data stored electronically. They come in various forms and serve different purposes, making them crucial in organizing, sorting, and retrieving information quickly. Understanding the concept of databases becomes even more critical in the context of information technology, particularly in fields such as computer science, software engineering, and data analytics. While this article focuses on Relational Databases, SQL, and Database Design, we begin with an overview of different types of databases.

Types of Databases

Databases can be broadly classified into four categories:

1. Relational Databases: Stores data in tables related to each other through common attributes.
2. NoSQL Databases: Does not store data in tables; instead, uses alternative data models like key-value pairs, document-oriented, or graph models.
3. Object-Oriented Databases: Stores data based on objects with properties and relations between them.
4. Time-Series Databases: Designed for storing and managing time-series data, often used in real-time applications.

Relational Databases

Relational Databases organize data in tables that consist of rows and columns. They establish relationships between these tables through primary keys and foreign keys. The structure inherently supports efficient querying and data manipulation operations. Popular relational database management systems (RDBMS) include MySQL, Oracle, PostgreSQL, Microsoft SQL Server, and IBM DB2.

Key characteristics of relational databases include:

• Scalability: As data grows, relational databases can adapt by adding more tables and relations.
• Data Integrity: Ensure consistency and accuracy by enforcing rules such as primary key uniqueness and referential integrity.
• Structured Query Language (SQL): Provides a standardized interface for interacting with and managing data.

SQL (Structured Query Language)

SQL is the standard programming language for interacting with relational databases. It offers data definition, manipulation, and control capabilities. Some key SQL features include:

• Data Definition Language (DDL): Used to create or modify database structures such as tables, indices, and views.
• Data Manipulation Language (DML): Allows querying data through statements like SELECT, UPDATE, INSERT, DELETE, etc.
• Transaction Management: Supports atomicity, consistency, isolation, and durability properties that ensure reliable storage of data changes.

Database Design

Database design is the process of creating a logical structure for storing and managing data in databases. It involves several stages:

1. Conceptual Model: Defines the high-level entities, relationships, and attributes needed to represent the problem domain. This stage aims at understanding user requirements and specifying what information needs to be stored.
2. Logical Data Model: Translates conceptual models into concrete schema definitions using precise concepts from relational theory. This phase ensures that all critical aspects of data are considered, including data integrity constraints, foreign keys, and normalization rules.
3. Physical Data Model: Maps logical data structures onto physical components such as files, directories, indexes, and access methods used by database systems. It also details the organization of these components on secondary storage devices like hard disks.

By following this structured approach, database designers can develop efficient storage solutions tailored to specific use cases while ensuring robustness and maintainability over time.