Comparison of Relational and NoSQL Databases

Introduction

• Databases are essential for storing, managing, and retrieving data efficiently.
• The two main types of databases are:
  • Relational Databases (SQL) – Use structured tables with relationships between data.
  • NoSQL Databases – Store unstructured, semi-structured, or distributed data.
• Choosing the right type of database depends on scalability, performance, flexibility, and use case.

What is a Relational Database?

Definition

• A Relational Database (SQL database) organizes data into tables with rows and columns.
• Uses Structured Query Language (SQL) to store, update, and retrieve data.
• Follows the ACID (Atomicity, Consistency, Isolation, Durability) principles for data integrity.

Characteristics of Relational Databases

1. Structured Data Storage
   • Stores data in predefined schemas (fixed table structures).
   • Example: A customer table with fields like Name, Email, and Phone Number.
2. Data Relationships
   • Tables are linked using primary and foreign keys.
   • Example: A sales order table linked to a customer table using a CustomerID.
3. ACID Compliance
   • Ensures data reliability and consistency, even in case of failures.
   • Example: A bank transaction either completes fully or does not happen at all.
4. Scalability
   • Typically scales vertically (adding more CPU, RAM, or storage to a single server).
   • Can struggle to handle huge amounts of data or high traffic loads.
5. Examples of Relational Databases
   • Microsoft SQL Server
   • MySQL
   • PostgreSQL
   • Oracle Database

Use Cases of Relational Databases

• Banking systems that require high accuracy in transactions.
• Enterprise resource planning (ERP) systems managing structured business data.
• Customer Relationship Management (CRM) tools where customer data is interrelated.

What is a NoSQL Database?

Definition

• NoSQL (Not Only SQL) databases store unstructured or semi-structured data in a flexible format.
• Designed for high scalability and fast data access, making them ideal for big data and real-time applications.

Characteristics of NoSQL Databases

1. Flexible Data Storage
   • Stores data in formats like documents, key-value pairs, graphs, and columns.
   • Example: A JSON document storing a user’s profile information.
2. Schema-Free
   • No need to define a fixed structure before storing data.
   • Example: A product catalog where each product has different attributes.
3. High Scalability
   • Scales horizontally (adds more servers instead of upgrading one).
   • Ideal for handling millions of requests per second.
4. BASE Model (Instead of ACID)
   • Basic Availability – Ensures availability even during failures.
   • Soft State – Data may change over time due to replication delays.
   • Eventual Consistency – Data is eventually synchronized across all copies.
5. Examples of NoSQL Databases
   • MongoDB (Document-Based)
   • Redis (Key-Value Store)
   • Cassandra (Column-Based)
   • Neo4j (Graph-Based)

Use Cases of NoSQL Databases

• Social media applications where data structure changes frequently.
• E-commerce websites handling product catalogs with varying attributes.
• Real-time analytics and IoT applications processing large volumes of data quickly.

Comparison of Relational and NoSQL Databases

Choosing Between Relational and NoSQL Databases

Use Relational Databases When:

✔ Data consistency and accuracy are critical (e.g., banking, finance).
✔ You need structured and predefined schemas (e.g., business applications).
✔ Complex relationships between data exist (e.g., CRM systems).

Use NoSQL Databases When:

✔ Handling massive data with high-speed access (e.g., analytics, IoT).
✔ Data structure changes frequently (e.g., social media, catalogs).
✔ You need high availability and scalability (e.g., global applications).

Quiz

1. Which of the following is a key feature of relational databases?
   A) Flexible document storage
   B) Uses SQL for querying data
   C) Schema-less data storage
   D) Designed for high scalability only
   E) Uses a key-value structure
2. NoSQL databases are best suited for which type of application?
   A) Banking and financial transactions
   B) Real-time analytics and big data applications
   C) Enterprise resource planning (ERP) systems
   D) Customer relationship management (CRM) software
   E) Payroll processing systems
3. What is the main difference between SQL and NoSQL databases in terms of scalability?
   A) SQL databases use horizontal scaling, while NoSQL uses vertical scaling
   B) SQL databases scale horizontally, and NoSQL databases scale vertically
   C) SQL databases are best for small applications only
   D) NoSQL databases scale horizontally across multiple servers, while SQL databases scale vertically by upgrading hardware
   E) NoSQL databases cannot scale at all
4. Which of the following is an example of a NoSQL database?
   A) MySQL
   B) Microsoft SQL Server
   C) MongoDB
   D) PostgreSQL
   E) Oracle Database
5. Why do NoSQL databases use the BASE model instead of ACID?
   A) To ensure data is always 100% consistent
   B) Because NoSQL databases do not use transactions
   C) To allow higher availability and eventual consistency in distributed systems
   D) Because NoSQL databases do not store relationships
   E) To prevent database failures

Answers

1. B – Uses SQL for querying data
   • Why others are incorrect?
     • A & C (Flexible storage, Schema-less) – These are features of NoSQL.
     • D & E (High scalability, Key-value structure) – NoSQL databases specialize in these.
2. B – Real-time analytics and big data applications
   • Why others are incorrect?
     • A, C, D, E – Require structured, transactional data management, best handled by SQL databases.
3. D – NoSQL databases scale horizontally across multiple servers, while SQL databases scale vertically by upgrading hardware
   • Why others are incorrect?
     • A & B – SQL databases do not natively use horizontal scaling.
     • C & E – NoSQL databases are highly scalable.
4. C – MongoDB
   • Why others are incorrect?
     • A, B, D, E – These are relational databases.
5. C – To allow higher availability and eventual consistency in distributed systems
   • Why others are incorrect?
     • A, B, D, E – BASE prioritizes availability over strict consistency.