Databases 📊

Databases 📊

A database is a structured collection of data, enabling easy access, management, and updates. It’s used to store and retrieve information in various applications.

Relational Models 🗂️

The relational model organizes data in tables with rows (records) and columns (attributes), linked by keys.

Key Concepts 🔑

• Table: A collection of related data organized in rows and columns.
• Row (Tuple): A single record in a table.
• Column (Attribute): A specific type of data in a table.

Keys 🛠️

• Primary Key: Unique identifier for a row.
• Foreign Key: Links a row in one table to a row in another.

Relationships 🔗

• One-to-One: One record in one table is linked to one in another.
• One-to-Many: One record in a table can link to multiple records in another.
• Many-to-Many: Multiple records in one table link to multiple in another.

Examples

One-to-One:
Users & User Profiles

Users Table	User Profiles Table
user_id (PK)	profile_id (PK)
username	user_id (FK)
email	first_name

One-to-Many:
Departments & Employees

Departments Table	Employees Table
department_id (PK)	employee_id (PK)
department_name	department_id (FK)

Many-to-Many:
Students & Courses

Students Table	Courses Table	Enrollment Table
student_id (PK)	course_id (PK)	enrollment_id (PK)
student_name	course_name	student_id (FK)
		course_id (FK)

Normalization 📉

Normalization minimizes data redundancy by dividing large tables into smaller ones, defining relationships.

SQL 📑

SQL is used to manage and query relational databases. Common commands: SELECT, INSERT, UPDATE, DELETE, CREATE, DROP.

Example

Customers Table:

CustomerID	Name	Email
1	Alice	alice@domain.com
2	Bob	bob@domain.com

Orders Table:

OrderID	CustomerID	Product	Quantity
101	1	Product A	2
102	2	Product B	3

In this example, CustomerID links the tables with a one-to-many relationship.

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