Relational Databases: An Overview

Introduction

A relational database organizes data into tables, making it one of the most widely used database models today. It represents data and their relationships using structured tables and supports manipulation and definition through SQL (Structured Query Language). This approach simplifies data organization, retrieval, and management.

1. Tables in Relational Databases

Tables, also known as relations, are the fundamental building blocks of a relational database. Each table comprises rows and columns:

Key Features:

• Columns (Attributes): Define the type of data stored (e.g., Name, Salary).
• Rows (Records): Contain the actual data entries (e.g., Einstein, Physics, 95000).

2. SQL: The Query Language

SQL (Structured Query Language) is the standard language for interacting with relational databases. It supports querying, inserting, updating, and deleting data.

Example SQL Queries:

SELECT name
FROM instructor
WHERE dept_name = 'History';

SELECT instructor.ID, department.dept_name
FROM instructor, department
WHERE instructor.dept_name = department.dept_name
AND department.budget > 95000;

3. Data-Definition Language (DDL)

DDL allows database administrators to define schemas, constraints, and tables. For instance:

CREATE TABLE department (
    dept_name CHAR(20),
    building CHAR(15),
    budget NUMERIC(12, 2)
);

4. Database Access via Application Programs

Relational databases often interact with application programs written in languages like C, C++, or Java. These programs use SQL queries to retrieve and manipulate data.

Access Methods:

• ODBC: A standard for connecting databases with C applications.
• JDBC: Java Database Connectivity for Java programs.

Conclusion

Relational databases are a cornerstone of modern data management. Understanding tables, SQL queries, and the role of DDL is essential for competitive exams like GATE, UGC NET, and ISRO. Mastering these concepts equips students and professionals to design efficient databases and solve real-world problems.