Unit 3: Database Concepts and Structured Query Language

1. Introduction to Database

What is a Database?

A database is an organized collection of structured data stored and accessed electronically. It provides efficient storage, retrieval, and management of large amounts of data.

Types of Database

2. SQL Basics

What is SQL?

SQL (Structured Query Language) is a standard language for managing relational databases. It allows users to create, retrieve, update, and delete data.

SQL Commands Categories

3. DDL Commands

CREATE TABLE

CREATE TABLE student (
    RollNo INT PRIMARY KEY,
    Name VARCHAR(50),
    Age INT,
    Marks FLOAT
);

ALTER TABLE

ALTER TABLE student ADD COLUMN Email VARCHAR(50);
ALTER TABLE student MODIFY COLUMN Marks DECIMAL(5,2);
ALTER TABLE student DROP COLUMN Email;

DROP TABLE

DROP TABLE student;
TRUNCATE TABLE student;

4. DML Commands

SELECT

SELECT * FROM student;
SELECT Name, Marks FROM student;
SELECT * FROM student WHERE Marks > 80;

INSERT

INSERT INTO student (RollNo, Name, Age, Marks) 
VALUES (101, 'Alice', 25, 85);

UPDATE

UPDATE student SET Marks = 90 WHERE RollNo = 101;

DELETE

DELETE FROM student WHERE RollNo = 101;

5. Querying Data

WHERE Clause

SELECT * FROM student WHERE Age > 20;
SELECT * FROM student WHERE Name LIKE 'A%';

ORDER BY and GROUP BY

SELECT * FROM student ORDER BY Marks DESC;
SELECT Age, COUNT(*) FROM student GROUP BY Age;

Aggregate Functions