Self-Learning Journey

Tracking my progress in IT

Links

SQL Notes

1. View all data
Used to display every record from a table.
```
SELECT * FROM students;
    
```

2. Insert data
Adds a new row into a table.

INSERT INTO students (id, name, age, grade)
VALUES (1, 'Alex', 20, 'A');

3. Update data
Modifies existing records in a table.

UPDATE students
SET grade = 'B'
WHERE name = 'Alex';

4. Delete data
Removes records from a table.

DELETE FROM students
WHERE name = 'Alex';

5. Filter records (WHERE)
Retrieves data based on conditions.
```
SELECT * FROM students
WHERE age > 18;
    
```
6. Sort records (ORDER BY)
Sorts results in ascending or descending order.
```
SELECT * FROM students
ORDER BY age ASC;
    
```

7. Count records
Returns the total number of rows.

SELECT COUNT(*) AS total_students
FROM students;

8. Average values
Calculates the average of a numeric column.
```
SELECT AVG(age) AS average_age
FROM students;
    
```

9. Group data
Groups records and applies aggregate functions.

SELECT grade, COUNT(*) AS total_students
FROM students
GROUP BY grade;

Python Notes

Python is a high-level programming language.
Supports procedural, object-oriented, and functional programming.

Basic syntax example:

# This is a comment
print("Hello, World!")
x = 10
if x > 5:
    print("x is greater than 5")

input() is used to take user input as text (string):

name = input("Enter your name: ")
print(name)

int() converts a string into an integer:

marks = int(input("Enter marks: "))

Basic arithmetic: +, -, *, / can be used for calculations:

total = math + science + english + hindi
percent = total / 4

f-strings are used for formatted printing:

print(f"Total: {total}")
print(f"Percentage: {percent}%")

Common data types: int, float, str, list, dict, tuple, set
Variables are used to store data:
```
name = "John"
age = 20
    
```

If-Else Condition is used to check conditions:

age = 18
if age >= 18:
    print("Adult")
else:
    print("Minor")

While Loop repeats code until condition becomes false:

while guess != number:
    print("Try again")

Random Number using random module:

import random
number = random.randint(1, 10)

Programs Learned:
- Greeting Program
- Number Guessing Game

Java Basics Notes

Java is a high-level, object-oriented programming language designed to be platform-independent.
Key Features of Java
- Object-Oriented
- Platform Independent (Write Once, Run Anywhere)
- Secure and Robust
- Automatic Memory Management (Garbage Collection)

Basic Java Program Structure

class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Java Data Types
- Primitive: int, float, double, char, boolean
- Non-Primitive: String, Array, Class, Interface

Variables

int age = 20;
double price = 99.99;
char grade = 'A';
boolean isActive = true;

Conditional Statements

int marks = 75;

if (marks >= 50) {
    System.out.println("Pass");
} else {
    System.out.println("Fail");
}

Loops

For Loop
While Loop
Do-While Loop

for (int i = 1; i <= 5; i++) {
    System.out.println(i);
}

Methods (Functions)

static void greet() {
    System.out.println("Hello from Java");
}

Object-Oriented Concepts (Basics)
- Class
- Object
- Encapsulation
- Inheritance
- Polymorphism
- Abstraction

Next Topics: Classes & Objects (deep), Constructors, Inheritance, Interfaces, Exception Handling.

HTML Notes

HTML stands for HyperText Markup Language.
Used to structure content on the web.

Basic elements:

<h1>Heading</h1>
<p>Paragraph</p>
<a href="url">Link</a>
<ul><li>List Item</li></ul>

HTML elements have tags and attributes.

CSS Notes

CSS stands for Cascading Style Sheets.
Used to style HTML content: colors, fonts, layout.

Basic example:

<style>
  body {
    background-color: lightblue;
  }
  h1 {
    color: navy;
  }
</style>

Selectors target HTML elements to apply styles.

Operating System (OS) Notes

Operating System (OS) is system software that manages hardware, software, and user interaction.
Main Functions of an OS
- Process management
- Memory management
- File system management
- Device management
- Security and access control
Types of Operating Systems
- Batch Operating System
- Time-Sharing Operating System
- Distributed Operating System
- Real-Time Operating System (RTOS)
- Network Operating System
Process Management
- A process is a program in execution
- Process States:
```
New → Ready → Running → Waiting → Terminated
        
```
- Context Switching – Switching CPU between processes
CPU Scheduling Algorithms
- FCFS – First Come First Serve
- SJF – Shortest Job First
- Round Robin
- Priority Scheduling
Memory Management
- RAM – Primary memory
- Virtual Memory – Uses disk as extended RAM
- Paging and Segmentation
Deadlock
- Occurs when processes wait indefinitely
- Deadlock Conditions:
  - Mutual Exclusion
  - Hold and Wait
  - No Preemption
  - Circular Wait
File System
- Manages data storage and retrieval
- Common file systems:
  - NTFS (Windows)
  - EXT4 (Linux)
  - FAT32
Security in OS
- User authentication and authorization
- Access control and permissions
- Process isolation

Next Topics: Linux commands, Windows internals, system calls, virtualization, containers.

JavaScript & TypeScript Notes (Smart Comparison)

JavaScript (JS) and TypeScript (TS) are closely related. TypeScript is a superset of JavaScript, meaning:
All JavaScript code is valid TypeScript code.

Main Difference
- JavaScript → Dynamic typing
- TypeScript → Static typing + JavaScript features

Basic Variable Declaration

JavaScript:
let age = 25;

TypeScript:
let age: number = 25;

Data Types

JavaScript:
let name = "Alex";
let isActive = true;

TypeScript:
let name: string = "Alex";
let isActive: boolean = true;

Functions

JavaScript:
function add(a, b) {
    return a + b;
}

TypeScript:
function add(a: number, b: number): number {
    return a + b;
}

Arrays

JavaScript:
let numbers = [1, 2, 3];

TypeScript:
let numbers: number[] = [1, 2, 3];

Objects

JavaScript:
let user = {
    name: "Sam",
    age: 22
};

TypeScript:
let user: {
    name: string;
    age: number;
} = {
    name: "Sam",
    age: 22
};

Why TypeScript Exists
- Catches errors at compile time
- Better code readability
- Great for large applications
- Excellent IDE support

Compilation Flow

TypeScript (.ts)
      ↓
Compiled to JavaScript (.js)
      ↓
Runs in Browser / Node.js

Where They Are Used
- JavaScript → Browsers, Node.js, web apps
- TypeScript → Angular, React, enterprise apps

Learning Strategy: Learn JavaScript fundamentals first, then move to TypeScript for safer and scalable code.

Networking Notes

Networking is the practice of connecting computers and devices to share data and resources.
Types of Networks
- LAN (Local Area Network) – Small area like home, office
- MAN (Metropolitan Area Network) – City-wide network
- WAN (Wide Area Network) – Large area like the Internet
Basic Networking Devices
- Router – Connects different networks
- Switch – Connects devices within a network
- Modem – Connects network to ISP
- Firewall – Protects network from threats
IP Address
- Unique identifier for a device on a network
- IPv4 example:
```
192.168.1.1
        
```
- IPv6 example:
```
2001:0db8:85a3::8a2e:0370:7334
        
```
Common Network Protocols
- HTTP / HTTPS – Web communication
- FTP – File transfer
- SMTP – Sending emails
- IMAP / POP3 – Receiving emails
- DNS – Converts domain names to IP addresses

Ports

HTTP  : 80
HTTPS : 443
FTP   : 21
SMTP  : 25
SSH   : 22

OSI Model (7 Layers)

7. Application
6. Presentation
5. Session
4. Transport
3. Network
2. Data Link
1. Physical

TCP vs UDP
- TCP – Reliable, connection-oriented
- UDP – Faster, connectionless

Network Security Notes

Network Security refers to protecting networks, devices, and data from unauthorized access, attacks, and misuse.
Goals of Network Security (CIA Triad)
- Confidentiality – Data is accessible only to authorized users
- Integrity – Data is not altered without permission
- Availability – Systems and data are accessible when needed
Common Network Threats
- Malware – Viruses, worms, trojans
- Phishing – Fake messages to steal credentials
- Man-in-the-Middle (MITM) – Intercepting communication
- Denial of Service (DoS / DDoS) – Overloading a system
- Packet Sniffing – Capturing network traffic
Firewalls
- Filter incoming and outgoing network traffic
- Types:
  - Packet-filtering firewall
  - Stateful firewall
  - Application-level firewall
  - Next-Generation Firewall (NGFW)
Encryption
- Protects data during transmission
- Symmetric Encryption – Same key for encryption & decryption
- Asymmetric Encryption – Public key & private key
- Examples:
```
HTTPS → TLS/SSL
SSH   → Secure remote access
        
```
Authentication Methods
- Password-based authentication
- Multi-Factor Authentication (MFA)
- Biometric authentication
- Certificate-based authentication
IDS & IPS
- IDS (Intrusion Detection System) – Detects attacks
- IPS (Intrusion Prevention System) – Detects and blocks attacks
Secure Network Practices
- Use strong passwords and MFA
- Keep systems and software updated
- Segment networks (VLANs)
- Disable unused ports and services
- Monitor logs and traffic

Common Secure Ports

HTTPS : 443
SSH   : 22
FTPS  : 990
SFTP  : 22

Next Steps

Gradually add more notes, code examples, and learning resources for each field.