Database Basics

What is a Database? #

A database is an organized collection of data that can be easily accessed, managed, and updated.

👉 Think of it like a digital storage system (similar to an Excel sheet, but more powerful).

Example #

• Student records
• Bank accounts
• E-commerce products

Why Do We Use Databases? #

• Store large amounts of data efficiently
• Retrieve data quickly
• Ensure data consistency
• Allow multiple users to access data

Types of Databases #

Basic Database Concepts #

Table #

• Data is stored in tables
• Example: Students table

Row (Record) #

• A single entry in a table
  👉 Example: 1, Alex, 20

Column (Field) #

• A category of data
  👉 Example: Name, Age

Primary Key #

• Unique identifier for each row
  👉 Example: ID

Database Management System (DBMS) #

Software used to manage databases

Examples:

• MySQL
• PostgreSQL
• SQLite

SQL Basics (Conceptual) #

What is SQL? #

SQL (Structured Query Language) is used to communicate with databases.

👉 It allows you to:

• Create data
• Read data
• Update data
• Delete data

SQL Core Commands (CRUD) #

SQL Concepts with Examples #

Create Table #

CREATE TABLE Students (
    ID INT PRIMARY KEY,
    Name VARCHAR(50),
    Age INT
);

👉 Creates a table named Students

Insert Data

INSERT INTO Students (ID, Name, Age)
VALUES (1, 'Alex', 20);

👉 Adds a new row

Select Data

SELECT * FROM Students;

👉 Retrieves all data

SELECT Name FROM Students;

👉 Retrieves specific column

Filter Data (WHERE)

SELECT * FROM Students
WHERE Age > 20;

👉 Shows students older than 20

Update Data

UPDATE Students
SET Age = 21
WHERE ID = 1;

👉 Updates specific record

Delete Data

DELETE FROM Students
WHERE ID = 1;

👉 Removes a row

Important SQL Concepts #

Constraints #

Rules applied to data:

• PRIMARY KEY → Unique
• NOT NULL → Cannot be empty
• UNIQUE → No duplicates

Joins (Conceptual) #

Used to combine multiple tables

👉 Example:

• Students table
• Courses table

Join them using a common column

Aggregation Functions #

Example:

SELECT AVG(Age) FROM Students;

Simple Workflow #

1. Create database
2. Create tables
3. Insert data
4. Query data using SQL
5. Update/Delete when needed