SQL – Day1

Introduction to Databases & SQL Basics

1. What is SQL?
SQL = Structured Query Language
It is used to store, manage, and retrieve data from relational databases.

SQL allows you to:

• Create databases
• Create tables
• Insert data
• Update and delete data
• Fetch data using queries

2. What is a Database?
A database is a collection of organised data.
Types of Databases:
1.Relational Database (RDBMS)

• Data stored in tables
• Uses SQL
• Examples: MySQL, PostgreSQL, Oracle, SQL Server 2.NoSQL Database
• Non-table structure (JSON, Key-Value, Document)
• Examples: MongoDB, Cassandra

3. What is a Table?
A table is a structure inside a database that stores data in:

• Rows → each entry (record)
• Columns → attributes (name, age, phone)

Example Table:Students

student_id	name	age	city
1	Arun	21	Chennai
2	Priya	22	Coimbatore
3	Karthi	23	Madurai

4. What is a Schema?
A schema is the blueprint/structure of a database.
It defines:

• Number of tables
• Columns
• Data types
• Relationships

SQL Commands

CREATE DATABASE
Used to create a new database.
CREATE DATABASE school;

USE DATABASE
Select the database to work inside.
USE school;

CREATE TABLE
Create a table with columns and data types.
CREATE TABLE students (
student_id INT,
name VARCHAR(50),
age INT,
city VARCHAR(50)
);

INSERT DATA
Insert records into the table.
INSERT INTO students (student_id, name, age, city)
VALUES (1, 'Arun', 21, 'Chennai');

Multiple insert:
INSERT INTO students VALUES
(2, 'Priya', 22, 'Coimbatore'),
(3, 'Karthi', 23, 'Madurai');

SELECT Data
Retrieve data from a table.
Fetch all columns
SELECT * FROM students;
Fetch specific columns:
SELECT name, city FROM students;