What is a Database?

A database is any organized collection of data. While a spreadsheet or document can store data, it is not ideal for large-scale or structured access.

For example:

Easy: Storing a small list of books in Excel.
Difficult: Managing 100,000 books with authors, publishers, and multiple copies using Excel.

What is a Relational Database?

A Relational Database Management System (RDBMS) organizes data into tables that are connected through relationships. Oracle is one of the most powerful RDBMS platforms.

Table Structure

Table Component	Description
Table	A collection of related data rows
Row	A single record
Column	A field that defines data type and label
Schema	A collection of tables and objects owned by a user

In Oracle:

A user owns a schema.
Two users can have tables with the same name because ownership is separate.

Why Use Relational Design?

Consider storing data about books and authors in one table. This causes data repetition if an author wrote multiple books.

Instead, normalize the data:

Create a separate AUTHORS table.
Link it to the BOOKS table using a foreign key.

ERD (Entity Relationship Diagram)

To understand how relational databases work, let’s look at a simple example with two tables: AUTHORS and BOOKS.

SQL Syntax to Create Tables:

CREATE TABLE authors (
  id         NUMBER PRIMARY KEY,
  first_name VARCHAR2(50),
  last_name  VARCHAR2(50)
);

CREATE TABLE books (
  isbn      CHAR(10) PRIMARY KEY,
  category  VARCHAR2(20),
  title     VARCHAR2(100),
  num_pages NUMBER,
  price     NUMBER,
  copyright NUMBER(4),
  author1   NUMBER CONSTRAINT books_author1
            REFERENCES authors(id)
);

AUTHORS Table

ID	First Name	Last Name
1	John	Smith
2	Alice	Brown

BOOKS Table

ISBN	Category	Title	Num Pages	Price	Copyright	Author ID
1001	Tech	Mastering PL/SQL	350	399	2023	1
1002	Fiction	The Silent Writer	280	299	2022	2

Example Query: JOIN Authors and Books:

SELECT b.title, a.first_name, a.last_name
FROM authors a, books b
WHERE b.author1 = a.id;

This joins the tables on the author1 foreign key, producing output like:

Title	First Name	Last Name
Mastering PL/SQL	John	Smith
The Silent Writer	Alice	Brown

Benefits of Relational Databases

Feature	Advantage
Redundancy Reduction	No repeated author info for each book
Data Integrity	Uses primary and foreign keys
Scalability	Easy to expand with more entities (e.g., Publisher)
Modularity	Separate logic for each entity (Authors, Books, etc.)