What is SQL

Definition (English)

SQL (Structured Query Language) is a standard programming language used to communicate with relational databases.

It allows users to:

• Store Data
• Retrieve Data
• Update Data
• Delete Data
• Manage Database

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Definition (Hindi)

SQL (Structured Query Language) एक Standard Language है जिसका उपयोग Database से Data को Store, Retrieve, Update, Delete और Manage करने के लिए किया जाता है।

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Simple Definition

SQL = Database की भाषा (Language of Database)

जैसे हम इंसानों से बात करने के लिए भाषा का उपयोग करते हैं, वैसे ही Database से बात करने के लिए SQL का उपयोग किया जाता है।

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Real-Life Example

Suppose a school has 10,000 students.

Question:

Show all students from CSE Department.

Without SQL:

❌ Search manually

With SQL:

SELECT * FROM Student
WHERE Department='CSE';

Result:

Database instantly returns the required students.

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Why SQL?

Without SQL

• Difficult searching
• Manual work
• Slow processing
• Error-prone

With SQL

• Fast
• Accurate
• Secure
• Easy to learn
• Standard language

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Where is SQL Used?

SQL is used in:

• Banking Systems
• Hospitals
• Schools
• Colleges
• Airlines
• Railway Reservation
• E-commerce
• Social Media
• Government Databases
• Mobile Apps
• Web Applications

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Popular Databases Using SQL

Database	Company
MySQL	Oracle
PostgreSQL	PostgreSQL Global Development Group
Oracle Database	Oracle
Microsoft SQL Server	Microsoft
SQLite	SQLite Consortium
MariaDB	MariaDB Foundation

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History of SQL

Year	Event
1970	Relational Model proposed by Edgar F. Codd
1974	SQL developed at IBM
1986	SQL became ANSI Standard
1987	SQL became ISO Standard

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Features of SQL

• Easy to Learn

• Simple Syntax
• Portable
• High Performance
• Secure
• Standard Language
• Supports Large Databases
• Supports Transactions
• Supports Constraints
• Supports Multiple Users

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Advantages of SQL

✔ Easy data retrieval

✔ Fast processing

✔ Less coding

✔ Secure

✔ Reliable

✔ Standard Language

✔ Supports millions of records

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Disadvantages

• Complex queries can be difficult.

• Vendor-specific extensions differ.
• Requires optimization for very large databases.

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SQL Architecture

          User

            │

            ▼

      SQL Query

            │

            ▼

     Database Engine

            │

            ▼

        Database

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SQL Categories

SQL commands are divided into five categories.

                 SQL

                  │

      ┌───────────┼────────────┐

      │           │            │

     DDL         DML          DQL

      │

      ├───────────────┐

      │               │

     DCL             TCL

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SQL Categories Explained

Category	Purpose
DDL	Defines database structure
DML	Manipulates data
DQL	Retrieves data
DCL	Controls permissions
TCL	Manages transactions

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DDL (Data Definition Language)

DDL changes the structure of database objects.

Commands:

• CREATE
• ALTER
• DROP
• TRUNCATE
• RENAME

Example:

CREATE TABLE Student
(
StudentID INT,
Name VARCHAR(50)
);

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DML (Data Manipulation Language)

DML manipulates data.

Commands:

• INSERT
• UPDATE
• DELETE

Example

INSERT INTO Student

VALUES(101,'Rahul');

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DQL (Data Query Language)

Used to retrieve data.

Command:

SELECT

Example

SELECT *

FROM Student;

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DCL (Data Control Language)

Controls permissions.

Commands:

• GRANT
• REVOKE

Example

GRANT SELECT

ON Student

TO User1;

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TCL (Transaction Control Language)

Manages transactions.

Commands

• COMMIT
• ROLLBACK
• SAVEPOINT

---

Example

COMMIT;

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SQL Data Types

Numeric

• INT

• BIGINT
• SMALLINT
• DECIMAL
• FLOAT
• DOUBLE

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Character

• CHAR
• VARCHAR
• TEXT

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Date & Time

• DATE

• TIME
• DATETIME
• TIMESTAMP

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Boolean

• BOOLEAN

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SQL Syntax Rules

• SQL keywords are not case-sensitive.

SELECT

Same as

select

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• Statements usually end with a semicolon.

SELECT * FROM Student;

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• String values use single quotes.

'Rahul'

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SQL Comments

Single-line:

-- This is a comment

Multi-line:

/*****

This is a comment

*****/

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Database Creation

CREATE DATABASE CollegeDB;

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Select Database

USE CollegeDB;

(MySQL and SQL Server)

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Create Table

CREATE TABLE Student
(
StudentID INT PRIMARY KEY,

Name VARCHAR(50),

Age INT,

Department VARCHAR(30)
);

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Table Structure

StudentID	Name	Age	Department
101	Rahul	20	CSE

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CRUD Operations

CRUD means:

Create

Read

Update

Delete

Operation	SQL Command
Create	INSERT
Read	SELECT
Update	UPDATE
Delete	DELETE

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SQL Workflow

Create Database

↓

Create Table

↓

Insert Data

↓

Retrieve Data

↓

Update Data

↓

Delete Data

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Complete Example

Create Table

CREATE TABLE Employee
(
EmpID INT PRIMARY KEY,

Name VARCHAR(50),

Salary INT
);

Insert Data

INSERT INTO Employee

VALUES

(101,'Rahul',50000),

(102,'Aman',45000);

Retrieve Data

SELECT *

FROM Employee;

Update

UPDATE Employee

SET Salary=55000

WHERE EmpID=101;

Delete

DELETE FROM Employee

WHERE EmpID=102;