A relational database is a type of database that stores and organizes data in tables, which are made up of rows and columns. Each table in a relational database represents an entity (e.g., customers, products) and is related to other tables through defined relationships. The relational model was introduced by Edgar F. Codd in 1970 and revolutionized how data is managed and structured in databases.

• Example: An e-commerce database may have separate tables for customers, orders, and products. These tables are related through keys that allow a query to combine data (e.g., finding the products each customer purchased).

Core Concepts of Relational Databases

1. Tables (Relations):

   • The primary structure in a relational database, where data is stored in rows and columns.
   • Each table has a unique name and contains data about a single type of entity.

2. Rows (Tuples):

   • Each row represents a single record in the table.
   • A row contains all the attribute values for a particular instance of the entity.

3. Columns (Attributes):

   • Columns represent the fields or properties of the entity (e.g., customer name, product price).
   • Each column has a specific data type and constraint.

4. Primary Key:

   • A unique identifier for each row in a table. It ensures that no duplicate records exist in the table.
   • Example: A CustomerID column that uniquely identifies each customer.

Benefits of Relational Databases

• Data Consistency and Integrity: Relationships between tables ensure consistent and accurate data through constraints and keys.
• Flexibility in Queries: SQL allows complex queries that can join multiple tables, filter data, and aggregate information.
• Security and Permissions: Robust user access control mechanisms ensure that only authorized users can view or modify data.
• Data Independence: Applications are separated from the physical data structure, which simplifies modifications without affecting the applications using the data.

Common Relational Database Management Systems (RDBMS)

• MySQL: Open-source, widely used for web applications.
• PostgreSQL: Advanced, open-source RDBMS with extensive features.
• Oracle Database: Known for its scalability and enterprise-level support.
• Microsoft SQL Server: A popular choice for businesses running Microsoft-based applications.
• SQLite: A lightweight, embedded relational database often used for mobile applications and small-scale projects.

We will learn more about relational databases in the upcoming chapters.