SQL (Structured Query Language) is a standard programming language used to manage and manipulate data in a Relational Database Management System (RDBMS).

Main Functions of SQL:

• Data Querying: Retrieve data using commands like SELECT.
• Data Insertion: Insert new records using INSERT.
• Data Update: Modify existing records using UPDATE.
• Data Deletion: Remove records using DELETE.
• Database Definition: Create and modify tables using CREATE, ALTER, DROP.

Example:

SELECT * FROM Students;

This command retrieves all records from the Students table.

API (Application Programming Interface) is a set of rules, protocols, and tools that allows different software applications to communicate with each other.

Purpose of API:

• To enable interaction between two software systems.
• To allow applications to request and exchange data.
• To simplify software development by reusing existing services.

How it Works:

An application sends a request to the API, and the API communicates with the server or system. The server processes the request and sends the response back through the API.

Example:

When you use a weather app, it fetches weather data from a server using a Weather API.

Recursion is a programming technique in which a function calls itself repeatedly to solve a smaller part of the same problem.

Main Components of Recursion:

• Base Case: The condition that stops the recursion.
• Recursive Case: The part where the function calls itself with a smaller input.

Example (Factorial in C):

int factorial(int n)
{
    if(n == 0)
        return 1;        // Base case
    else
        return n * factorial(n - 1);  // Recursive call
}

Explanation: The function keeps calling itself with (n-1) until n becomes 0, then it stops.

DNS (Domain Name System) uses Port 53 for communication.

Details:

• UDP Port 53: Used for most DNS queries and responses (faster and lightweight).
• TCP Port 53: Used for zone transfers and large DNS responses.