DEV Community: VINOTH

Credit Card Validation Using Python While Loop – Luhn Algorithm

VINOTH — Fri, 28 Aug 2026 16:17:43 +0000

How to Validate a Credit Card Number Using Python and the Luhn Algorithm?

no = 4532015112830366

total = 0
count = 0

while no > 0:
    digit = no % 10
    no = no // 10


    if count % 2 == 1:
        digit = digit*2


        if digit > 9:
            digit = digit % 10 + digit // 10

    total += digit
    count += 1

if total % 10 == 0:
    print("Valid credit card")    
else:
    print("Invalid credit card")

o/p:

Valid credit card

Write a Python program to validate a credit card number using the Luhn Algorithm. The program should process the digits from right to left, double every second digit, reduce two-digit results by adding their digits, calculate the total, and determine whether the credit card number is valid.

Python Lcm,Hcf Learn

VINOTH — Thu, 27 Aug 2026 03:49:02 +0000

1)There are four Mobile Phones in a house. At 5 a.m, all the four Mobile Phones will ring together. Thereafter, the first one rings every 15 minutes, the second one rings every 20 minutes, the third one rings every 25 minutes and the fourth one rings every 30 minutes. At what time, will the four Mobile Phones ring together again?

def find_lcm(num1, num2, num3, num4):
    lcm = num1
    while True:
        if lcm % num1 == 0 and lcm % num2 == 0 and lcm % num3 == 0 and lcm % num4 == 0:
            return lcm


        lcm +=1


num1 = 15
num2 = 20
num3 = 25
num4 = 30

result = find_lcm(num1, num2, num3, num4)
print(result)

o/p:

2)A book seller has 175 English books, 245 Science books and 385 Mathematics books. He wants to sell the books in a box, subject-wise in equal numbers. What will be the greatest number of the boxes required? Also find the number of books for each subject in a box.

def find_hcf(num1, num2, num3):
    div = 1
    hcf = 1

    while div <= num1:
        if num1 % div == 0 and num2 % div == 0 and num3 % div == 0:
            hcf = div

        div +=1

    return hcf        

num1 = 175
num2 = 245
num3 = 385

result = find_hcf(num1, num2, num3)
print(result)
print("Greatest number of boxes:", result)
print("English in each boxes:", num1 // result)
print("Science in each boxes:", num2 // result)
print("Mathematics in each boxes:", num3 // result)

0/p:

35
Greatest number of boxes: 35
English in each boxes: 5
Science in each boxes: 7
Mathematics in each boxes: 11

3)Two numbers are said to be amicable numbers if the sum of the factors of one number (except the number itself) gives the other number.
The numbers 220 and 284 are amicable, since the sum of the factors of 220 (except 220) i.e., 1+2+4+5+10+11+20+22+44+55+110 = 284 and the sum of the factors of 284 (except 284) i.e., 1+2+ 4+71+142 = 220. Check whether 1184 and 1210 are amicable numbers.

def find_factors(no):

    div = 1
    total = 0

    while div < no:

        if no % div == 0:
            # print(f'{div} is a factors of {no}')

            total += div

        div +=1

    return total        

# result = find_factors(1184)

# print( result)


num1 = 1184
num2 = 1210

sum1 = find_factors(num1)
sum2 = find_factors(num2)

#print(sum1)
#print(sum2)
print("num1:1184 =",sum1)
print("num2:1210 =",sum2)

o/p:

num1:1184 = 1210
num2:1210 = 1184

React useState Hook - Day1

VINOTH — Wed, 26 Aug 2026 13:34:57 +0000

1) Toggle Button:
You build a button that switches between:
"ON" ↔ "OFF"
What type of state should you use?
What is the best initial value?

import { useState } from "react"

function Toggle() {

  const [status, setStatus] = useState("OFF");

    function togglebtn() {

            if (status === "OFF") {
                setStatus("ON");
            }else{
                setStatus("OFF");
            }
    }

    return(
        <div>
            <h1>{status}</h1>
            <button onClick={togglebtn}>Toggle</button>
        </div>
    )
}

export default Toggle

2) Input Field Value:
You have a text input.
User types name and you want to display:
Hello, Vinoth
Why must the input value be stored in useState?
What happens if you use a normal variable?

import { useState } from "react"

function Name() {

    const [name, setName] = useState("");

    function handle(e) {

        setName(e.target.value);

    }

    return(
        <div>
            <input 

                 value={name}
                 onChange={handle}
            />
            <h1>Hello, {name}</h1>
        </div>
    )
}

export default Name

3) Show/Hide Text:
You want to show paragraph only when button is clicked.
What kind of state works best?
Why boolean is suitable here?

import { useState } from "react"

function Text() {

  const [show, setShow]= useState(false);

    function handle () {

        if (show === false) {
            setShow(true)
        }else{
            setShow(false)
        }

    }

    return(
        <div>
           <button onClick={handle}>
            show / hide
           </button>

           {show && <p>Hello! This is my paragraph.</p>}
        </div>
    )
}

export default Text

4) Character Counter:
User types in textarea. You show number of characters.
How do you track text length?
Should you store both text and length in state?

import { useState } from "react"

function Count() {

  const [text, setText]= useState("");



    return(
        <div>
          <textarea 

          value={text}
          onChange={(e)=>setText(e.target.value)}

          />

          <p>Characters: {text.length}</p>
        </div>
    )
}

export default Count

5) Form with Multiple Inputs
You have 5 input fields (name, email, phone, city, password).
Better to use:
5 separate useState?
OR one object state?
Why?
What problem happens if you update object state incorrectly?

import { useState } from "react";

function FormHandling() {


 const [form, setForm] = useState({
name: "",
email:"",
phone:"",
city:"",
password:""
})

function handle(e) {
    setForm({...form, [e.target.name]: e.target.value })
    console.log(e.target.value);

}


    return(
        <div>

            <form >

                <label htmlFor="name">name</label>
                <input type="text" id="name" name = "name" onChange={handle}/>

                <label htmlFor="email">email</label>
                <input type="email" id="email" name="email" onChange={handle}/>

                <label htmlFor="phone">phone</label>
                <input type="phone" id="phone" name="phone" onChange={handle}/>

                <label htmlFor="city">city</label>
                <input type="city" id="city" name="city" onChange={handle}/>

                <label htmlFor="password">pass</label>
                <input type="password" id="password" name="password" onChange={handle}/>

            </form>
            <h1>{`Name: ${form.name}, Email: ${form.email}, phone: ${form.phone}, city: ${form.city} ,password: ${form.password}`}</h1>

        </div>
    )
}

export default FormHandling;

6) Checkbox Selection List
User can select multiple skills:
☐ React
☐ Node
☐ Java
☐ SQL
What should be the state type?
How will you add/remove values from state array?

import { useState } from "react"

function Checkbox() {

    const [skills, setSkills] = useState([])

    function handle(e) {


        if (e.target.checked) {
            setSkills([...skills, e.target.value])
        } else {
            // skills.filter((skill) => e.target.value != skill)
            setSkills(
                skills.filter((skill) => skill !== e.target.value)
            );
        }
    }

    return (
        <div>

            <input type="checkbox" value={"sql"} onChange={handle} />sql <br />
            <input type="checkbox" value={"java"} onChange={handle} /> java  <br />
            <input type="checkbox" value={"node"} onChange={handle} /> node  <br />
            <input type="checkbox" value={"react"} onChange={handle} /> react


            <h2>Selected Skills:</h2>

            {skills.map((skill) => {
                return <p key={skill}>{skill}</p>;
            })}

        </div>
    )
}

export default Checkbox;

React useState Hook

VINOTH — Wed, 26 Aug 2026 13:24:55 +0000

The useState hook allows functional components in React to store and manage data that can change over time. It is simple to use and ideal for handling basic state updates within a component.

It lets you add state variables to functional components.
It is best suited for simple and straightforward state updates.
The hook must be imported from React before using it.

Syntax

const [state, setState] = useState(initialState)

state: It is the value of the current state.
setState: It is the function that is used to update the state.
initialState: It is the initial value of the state.

Example:

import { useState } from "react"

function Count() {

  const [count, setCount] = useState(0);

    function incerement () {
        setCount(count+1)
    }

    function decerement() {
        setCount(count-1)
    }

    function reset() {
        setCount(0)
    }
    return(
        <div>
            <h1>Counter app</h1>
            <h3>count: {count}</h3>
            <button onClick={incerement}>+</button>
            <button onClick={decerement}>-</button>
            <button onClick={reset}>reset</button>
        </div>
    )
}

export default Count

Closure in JavaScript

VINOTH — Mon, 24 Aug 2026 16:30:54 +0000

A closure is created when a function remembers the variables from its outer scope, even after the outer function has finished executing.

How Closures Work

An outer function creates a local variable.
An inner function inside the outer function uses that variable.
The outer function returns the inner function.
The variable stays in memory because the inner function still needs it.

 <script>

        function bank() {

            let min_balance = 500;

            const actions = {

                deposit: function (amt) {
                    min_balance = min_balance + amt;
                },

                withdraw: function (amt) {
                    min_balance = min_balance - amt;
                },
                checkbalance: function () {
                    console.log(min_balance);

                }



            }
            return actions;
        }

        const customer1 = bank();
        customer1.deposit(100);
        customer1.checkbalance();
        customer1.withdraw(200);
        customer1.checkbalance();

    </script>

Synchronous vs Asynchronous vs Promise in JavaScript

VINOTH — Sun, 23 Aug 2026 11:48:13 +0000

In JavaScript, synchronous means code runs line-by-line in order, asynchronous means code can start a long-running task and move on immediately without waiting, and a Promise is a modern JavaScript object used to manage those asynchronous tasks cleanly.

Think of it like ordering food at a restaurant:

Synchronous: You stand in line, order, and wait at the register until your food is cooked. The line behind you is completely blocked.
Asynchronous: You order, get a buzzer, and sit down. You can check your phone while your food cooks.
Promise: The buzzer itself. It is a token that represents the future delivery of your meal.

1. Synchronous JavaScript (Sync):

JavaScript is synchronous and single-threaded.
It executes one command at a time in a strict sequence.
If a line of code takes 10 seconds to compute, the entire browser freezes and waits.

Characteristics: Sequential, predictable, blocking.

console.log("A");
console.log("B");
console.log("C");

o/p:

A
B
C

Flow:

A → finish
    ↓
B → finish
    ↓
C → finish

2. Asynchronous JavaScript (Async):

Asynchronous programming allows JavaScript to offload long-running tasks (like fetching data from a server or waiting for a timer) to the browser background.
The main program keeps running without stalling.

Characteristics: Non-blocking, handles concurrent actions, relies on a callback queue.

console.log("A");

setTimeout(() => {
    console.log("B");
}, 2000);

console.log("C");

o/p:

A
C
B

Why?

A → executes immediately

setTimeout → waits for 2 seconds

C → executes immediately

After 2 seconds → B executes

3. Promises (The Async Manager):

Historically, asynchronous tasks used basic callback functions. However, nesting multiple callbacks inside each other created unreadable code known as "Callback Hell".
A Promise is a placeholder for a value that you don't have yet but will receive in the future.

A Promise always exists in one of three states:

Pending: The background task is still working.
Fulfilled: The task completed successfully, and you get the result.
Rejected: The task failed, and you get an error message.

For example, imagine ordering food:

Order food
    ↓
Pending
    ↓
Food ready → Success
    OR
Problem → Failure

A Promise has three states:

Pending
   ↓
   ├── Fulfilled ✅
   │
   └── Rejected ❌

Example:

const promise = new Promise((resolve, reject) => {

    let success = true;

    if (success) {
        resolve("Success");
    } else {
        reject("Failed");
    }

});

4. Handling a Promise:

We can use .then() and .catch().

promise
    .then((result) => {
        console.log(result);
    })
    .catch((error) => {
        console.log(error);
    });

.then()

Used when the Promise is successful.

.catch()

Used when the Promise fails.

5. Promise with fetch():

fetch() is commonly used to get data from an API.

fetch("https://fakestoreapi.com/products")
    .then((response) => response.json())
    .then((data) => {
        console.log(data);
    })
    .catch((error) => {
        console.log(error);
    });

Flow:

fetch()
   ↓
Promise
   ↓
Server Response
   ↓
response.json()
   ↓
Data

Easy way to remember:

Synchronous
→ WAIT → NEXT

Asynchronous
→ DON'T WAIT → NEXT

Promise
→ RESULT WILL COME LATER

async/await
→ EASY WAY TO HANDLE PROMISE

Python - Neon, Strong, Duck, and Spy Number programs

VINOTH — Sun, 23 Aug 2026 05:52:26 +0000

Neon Number

1)Write a Python program to check whether a given number is a Neon Number or not.

Example:

9 × 9 = 81

8 + 1 = 9

def sum_of_digits(no):
    sum = 0
    while no > 0:
        sum = sum + no%10
        no = no//10
    return sum

number = 9 
square = number ** 2 #number * number 
sum = sum_of_digits(square)
if number == sum: 
    print('Neon Number')

o/p:

Neon Number

Strong Number

2)Write a Python program to check whether a given number is a Strong Number or not.

    def find_factorial(no):
     factorial = 1
    while no > 0:
        factorial *= no #factorial = factorial * no
        no-=1 #   no = no - 1

    return factorial 

def digits(no): #145
    total = 0
    while no > 0:
        digit = no % 10
        factorial = find_factorial(digit) 
        total += factorial #total = total + factorial
        #print(f'factorial of {digit} is {factorial}')
        no = no//10
    return total 

number = int(input("Enter no. "))
result = digits(number) 
if result == number: 
    print("Strong Number")

o/p:

Strong Number

Duck Number

3) Write a Python program to check whether a given number is a Duck Number or not.

    no = input("Enter no.")
if no[0] == '0':
    print('Not a Duck Number')
else:
    if '0' in no:
        print("Duck Number")

o/p:

Duck Number

Spy Number

4) Write a Python program to check whether a given number is a Spy Number or not.

 def sum_of_digits(no):
    sum = 0
    multiply = 1

    while no > 0:
        sum = sum + no % 10
        multiply = multiply * (no % 10)
        no = no // 10

    return sum, multiply

no = 1411
result1, result2 = sum_of_digits(no)
print('Spy Number: ', result1==result2)

o/p:

Spy Number:  False

Software Testing Life Cycle (STLC)

VINOTH — Thu, 20 Aug 2026 11:05:02 +0000

The Software Testing Life Cycle (STLC) is a step-by-step process used by quality assurance teams to test software. It has six main phases: Requirement Analysis, Test Planning, Test Case Development, Test Environment Setup, Test Execution, and Test Closure.

1. Requirement Analysis:

Read the project rules and documents.
Find out what features to test.
Talk to the team if anything is unclear.

2. Test Planning:

Write down the test strategy and scope.
Guess how much time and money it will take.
Pick tools and assign tasks.

3. Test Case Development:

Write clear test steps and expected results.
Prepare test data.
Check the tests with team leads.

4. Test Environment Setup:

Build the hardware and software systems for testing.
Prepare test servers and databases.
Check if the environment is ready.

5. Test Execution:

Run the tests.
Match real results with expected results.
Write bug reports when things fail.

6. Test Closure:

Make sure all bugs are fixed or tracked.
Write a final test summary report.
Clean up the test area.

Python Practice Program

VINOTH — Wed, 19 Aug 2026 16:18:39 +0000

1) Write a Python program to check whether the next number after a given number is a prime number or not.

def find_prime(no):
    div = 2
    while div <= no//2:
        if no % div == 0:
            return False
        div+=1
    else:
        return True

prime1 = 7
prime2 = prime1+1

result = find_prime(prime1+1)

if result == True:
    print(result)

else:
    print(f"{prime2} is not a prime number.")

o/p:

8 is not a prime number.

Python Learn - Function

VINOTH — Mon, 17 Aug 2026 16:43:09 +0000

1) Secret VIP Numbers

A security system assigns special numbers to the first few VIP lockers. A number is considered a VIP number if it can be divided exactly by only 1 and itself. The security officer wants the numbers of the first 5 VIP lockers. Write a Python program to display those 5 numbers.

def find_vip_number(no):
    div = 2
    while div <= no//2:
        if no % div == 0:
            return 'not VIP'
        div+=1
    else:
        return 'VIP'

no = 2
count = 0
while count < 5:
    result = find_vip_number(no) #Function Calling Statement 
    if result == 'VIP':
        print(no)
        count+=1
    no = no+1

o/p:

2) The Special Numbers
A teacher is preparing a Number Exhibition for students. She writes the numbers 1 to 20 on 20 cards. She wants to select only the special cards. A card is special if its number can be divided exactly by only two numbers: 1 and the number itself.

The teacher asks the students:
“Check all the cards from 1 to 20 and display the numbers that are special.”

def find_vip_number(no):
    div = 2
    while div <= no//2:
        if no % div == 0:
            return 'not VIP'
        div+=1
    else:
        return 'VIP'

no = 1
while no <= 20:
    result = find_vip_number(no) #Function Calling Statement 
    if result == 'VIP':
        print(no)
    no = no+1

o/p:

3) You have Rs. 100 /- One chocolate costs Rs. 5. Every time you buy a chocolate, you get one wrapper. You can exchange 3 wrappers for 1 additional chocolate. What is the maximum number of chocolates you can have with Rs. 100?

chocolate   = 20
wrapper     = 20

while wrapper >= 3:
    wrapper = wrapper - 3
    chocolate = chocolate + 1
    wrapper = wrapper + 1
else:
    print(chocolate)

o/p:

4) There is one person called Viyan. He is a Software Engineer. He employs a maid for cooking. One day, the maid prepared n number of chapathis and kept in a hot box. Viyan ate those chapathis and the count is as follows:
* For Morning breakfast, he completed 1/3 number of chapathis in the hot box.
* For Lunch, He had 1/3 of what was there in the hot box.
* For Dinner, again he took and ate 1/3 number of chapathis present in the box.

The next day morning, When the maid checked the number of chapathis remaining, it was 8. What was the number of chapathis, She made - in total?

chapathi = 8
count = 0

while count < 3:
    chapathi = chapathi * 3 // 2
    count += 1

print(chapathi)

o/p:

Software Testing

VINOTH — Mon, 17 Aug 2026 11:28:37 +0000

1. What is a Test Case?

A test case is a detailed document containing a set of conditions, steps, inputs, and expected results used by quality assurance (QA) professionals to verify if a software application behaves correctly.

Example:
For a login page, a test case can be:

Enter a valid username.
Enter a valid password.
Click the Login button.
Expected result: The user should successfully log in.

Main Types of Test Cases

Functional Test Cases: Checks if a feature performs exactly as business requirements dictate (e.g., adding an item to a cart updates the total).
Integration Test Cases: Verifies that two or more interacting software modules or APIs work smoothly together.
Negative Test Cases: Tests how the system handles invalid input or abnormal conditions to check error handling (e.g., typing a letters into a phone number field).
Security & Performance Test Cases: Checks the software's data integrity limits, load thresholds, and potential system vulnerabilities.

2. What is a Test Scenario?

The fundamental difference is that a test scenario defines what to test, while a test case defines how to test it.

Example:

"Test the Login functionality."

A single test scenario can contain multiple test cases.

3. What are Negative Test Cases?

Negative test cases verify how a software application behaves when given invalid inputs, unexpected actions, or error conditions.

Examples:

Entering an incorrect password.
Leaving the username field empty.
Entering an invalid email address.

4. What are Positive Test Cases?

Positive test cases are instructions that check if software works the right way when you give it correct and expected data.

Key Features

Uses valid, expected inputs
Follows standard user steps
Tests ideal conditions
Confirms correct outputs

What is the difference between positive and negative test cases?

Positive test cases check if a system works with valid data. Negative test cases check how a system handles invalid data or errors. Both are vital for software quality.

Positive Test Cases

What they do: Test normal, expected behavior.
Input type: Valid data.
Goal: Confirm the system performs correctly.
Example (Login): Enter a valid username and correct password. The system logs you in.
Example (Age field): Enter 25 into a field that takes ages 1 to 100. The system accepts it.

Negative Test Cases

What they do: Test error handling and system safety.
Input type: Invalid or unexpected data.
Goal: Ensure the system fails gracefully without crashing.
Example (Login): Enter a wrong password. The system shows an error message and denies access.
Example (Age field): Enter -5 or abc. The system blocks the entry and shows an error.

6. What is Unit Testing?

A unit test is a small block of code written by developers to isolate and verify that a single, specific component of an application (like a function or method) behaves correctly.

7. What is Integration Testing?

Integration testing is a software testing phase where individual modules, components, or applications are combined and tested as a group.

Common Approaches

Big Bang: All components are integrated simultaneously and tested together.
Top-Down: Testing flows from top-level modules to lower-level ones using "stubs."
Bottom-Up: Testing flows from lowest-level components upward using "drivers."
Sandwich (Hybrid): A combination of top-down and bottom-up strategies.

9. Difference Between Stub and Driver

In software testing, stubs and drivers are temporary dummy

A stub simulates a lower-level module called by the code under test.
A driver simulates a higher-level module that calls the code under test.

Top-Down → Stub

Bottom-Up → Driver

10. Difference Between Error, Bug and Defect

An Error is a mistake made by a developer or programmer.
A Bug is an issue in the software caused by an error.
A Defect is a deviation between the actual result and the expected result or requirement.

11. Difference Between Top-Down and Bottom-Up Testing

In Top-Down Integration Testing, testing starts from the higher-level modules and moves toward the lower-level modules. Stubs are used for unavailable lower-level modules.
In Bottom-Up Integration Testing, testing starts from the lower-level modules and moves toward the higher-level modules. Drivers are used for unavailable higher-level modules.

12. Difference Between BRS, SRS and FRS

BRS – Business Requirement Specification: Describes what the business needs.
SRS – Software Requirement Specification: Describes what the software should provide.
FRS – Functional Requirement Specification: Describes the detailed functional behavior of the system.

SQL Multiple JOIN

VINOTH — Sun, 16 Aug 2026 17:18:07 +0000

Scenario - Students -> Student Courses -> Trainers -> Courses

Level 1: Difficulty Level: Easy

Display the course name and trainer name for every course.

cinemas=# select c.course_name, t.trainer_name
cinemas-# from courses c
cinemas-# join trainers t
cinemas-# on c.trainer_id = t.trainer_id;

o/p:

  course_name    | trainer_name 
------------------+--------------
 Python           | Vijay
 Java             | Muthu
 PostgreSQL       | Arun
 Spring Boot      | Muthu
 React            | Prithvi
 Software Testing | Vallarasu
 AWS              | Vijay
(7 rows)

Display: ◦ Course Name ◦ Trainer Name ◦ Trainer Specialization

cinemas=# select c.course_name, t.trainer_name, t.specialization 
from courses c
join trainers t
on c.trainer_id = t.trainer_id;

o/p:

   course_name    | trainer_name |   specialization   
------------------+--------------+--------------------
 Python           | Vijay        | Python & AWS
 Java             | Muthu        | Java & Spring Boot
 PostgreSQL       | Arun         | PostgreSQL
 Spring Boot      | Muthu        | Java & Spring Boot
 React            | Prithvi      | React
 Software Testing | Vallarasu    | Software Testing
 AWS              | Vijay        | Python & AWS
(7 rows)

Display all courses taught by Vijay.

cinemas=# select c.course_name   
from courses c
join trainers t
on c.trainer_id = t.trainer_id
cinemas-# where t.trainer_name = 'Vijay';

o/p:

 course_name 
-------------
 Python
 AWS
(2 rows)

Display all courses taught by trainers having more than 5 years of experience.

cinemas=# select c.course_name, t.trainer_name 
from courses c
join trainers t
on c.trainer_id = t.trainer_id
where t.experience_years > 5;

o/p:

   course_name    | trainer_name 
------------------+--------------
 Python           | Vijay
 Java             | Muthu
 PostgreSQL       | Arun
 Spring Boot      | Muthu
 Software Testing | Vallarasu
 AWS              | Vijay
(6 rows)

Display the course name and fee along with the trainer name.

cinemas=# select c.course_name, c.fee, t.trainer_name 
from courses c
join trainers t
on c.trainer_id = t.trainer_id;

o/p:

   course_name    |   fee    | trainer_name 
------------------+----------+--------------
 Python           | 25000.00 | Vijay
 Java             | 30000.00 | Muthu
 PostgreSQL       | 20000.00 | Arun
 Spring Boot      | 28000.00 | Muthu
 React            | 22000.00 | Prithvi
 Software Testing | 18000.00 | Vallarasu
 AWS              | 32000.00 | Vijay
(7 rows)

Level 2 — Student + Course

Difficulty: Easy

Display the student name and course name for every enrollment.

cinemas=# select student_name, c.course_name
from students s
join student_courses sc
on s.student_id = sc.student_id
join courses c
on sc.course_id = c.course_id;

o/p:

 student_name |   course_name    
--------------+------------------
 Arul         | Python
 Arul         | AWS
 Kavin        | Java
 Venba        | PostgreSQL
 Venba        | Spring Boot
 Kanmani      | React
 Mathi        | Software Testing
 Paari        | Python
 Paari        | Spring Boot
 Kathir       | Java
 Seyon        | React
(11 rows)

Display: ◦ Student Name ◦ City ◦ Course Name ◦ Enrollment Date

cinemas=# select student_name, s.city, c.course_name, sc.enrolled_date 
from students s
join student_courses sc
on s.student_id = sc.student_id
join courses c
on sc.course_id = c.course_id;

o/p:

 student_name |    city    |   course_name    | enrolled_date 
--------------+------------+------------------+---------------
 Arul         | Chennai    | Python           | 2026-01-10
 Arul         | Chennai    | AWS              | 2026-02-15
 Kavin        | Madurai    | Java             | 2026-01-12
 Venba        | Chennai    | PostgreSQL       | 2026-01-15
 Venba        | Chennai    | Spring Boot      | 2026-02-01
 Kanmani      | Coimbatore | React            | 2026-01-20
 Mathi        | Salem      | Software Testing | 2026-02-05
 Paari        | Chennai    | Python           | 2026-01-25
 Paari        | Chennai    | Spring Boot      | 2026-02-10
 Kathir       | Trichy     | Java             | 2026-02-12
 Seyon        | Coimbatore | React            | 2026-02-20
(11 rows)

Find all courses taken by Muthu.

cinemas=# select c.course_name
cinemas-# from courses c
cinemas-# join trainers t
cinemas-# on c.trainer_id = t.trainer_id
cinemas-# where t.trainer_name = 'Muthu';

o/p:

 course_name 
-------------
 Java
 Spring Boot
(2 rows)

Find all students who have enrolled in Java.

cinemas=# select student_name, c.course_name
from students s
join student_courses sc
on s.student_id = sc.student_id
join courses c
on sc.course_id = c.course_id
where c.course_name = 'Java';

o/p:

 student_name | course_name 
--------------+-------------
 Kavin        | Java
 Kathir       | Java
(2 rows)

Find all students from Chennai and the courses they have enrolled in.

cinemas=# select student_name, c.course_name
from students s
join student_courses sc
on s.student_id = sc.student_id
join courses c
on sc.course_id = c.course_id
where s.city = 'Chennai';

o/p:

 student_name | course_name 
--------------+-------------
 Arul         | Python
 Arul         | AWS
 Venba        | PostgreSQL
 Venba        | Spring Boot
 Paari        | Python
 Paari        | Spring Boot
(6 rows)

Level 3 - Three/Four Table JOIN

Difficulty Level: Intermediate:

Display Student Name, Course Name and Trainer Name

cinemas=# select s.student_name, c.course_name, t.trainer_name
from students s
join student_courses sc
on s.student_id = sc.student_id
join courses c
on sc.course_id = c.course_id
join trainers t
on c.trainer_id = t.trainer_id;

plaintext
o/p:

 student_name |   course_name    | trainer_name 
--------------+------------------+--------------
 Arul         | Python           | Vijay
 Arul         | AWS              | Vijay
 Kavin        | Java             | Muthu
 Venba        | PostgreSQL       | Arun
 Venba        | Spring Boot      | Muthu
 Kanmani      | React            | Prithvi
 Mathi        | Software Testing | Vallarasu
 Paari        | Python           | Vijay
 Paari        | Spring Boot      | Muthu
 Kathir       | Java             | Muthu
 Seyon        | React            | Prithvi
(11 rows)

plaintext

Display Student Name, Student City, Course Name, Trainer Name

cinemas=# select s.student_name, s.city, c.course_name, t.trainer_name
from students s
join student_courses sc
on s.student_id = sc.student_id
join courses c
on sc.course_id = c.course_id
join trainers t
on c.trainer_id = t.trainer_id;

plaintext
o/p:

 student_name |    city    |   course_name    | trainer_name 
--------------+------------+------------------+--------------
 Arul         | Chennai    | Python           | Vijay
 Arul         | Chennai    | AWS              | Vijay
 Kavin        | Madurai    | Java             | Muthu
 Venba        | Chennai    | PostgreSQL       | Arun
 Venba        | Chennai    | Spring Boot      | Muthu
 Kanmani      | Coimbatore | React            | Prithvi
 Mathi        | Salem      | Software Testing | Vallarasu
 Paari        | Chennai    | Python           | Vijay
 Paari        | Chennai    | Spring Boot      | Muthu
 Kathir       | Trichy     | Java             | Muthu
 Seyon        | Coimbatore | React            | Prithvi
(11 rows)

plaintext

Display Student Name, Course Name, Trainer Name, Trainer Specialization

cinemas=# select s.student_name, c.course_name, t.trainer_name, t.specialization               
from students s
join student_courses sc
on s.student_id = sc.student_id
join courses c
on sc.course_id = c.course_id
join trainers t
on c.trainer_id = t.trainer_id;

plaintext
o/p:

 student_name |   course_name    | trainer_name |   specialization   
--------------+------------------+--------------+--------------------
 Arul         | Python           | Vijay        | Python & AWS
 Arul         | AWS              | Vijay        | Python & AWS
 Kavin        | Java             | Muthu        | Java & Spring Boot
 Venba        | PostgreSQL       | Arun         | PostgreSQL
 Venba        | Spring Boot      | Muthu        | Java & Spring Boot
 Kanmani      | React            | Prithvi      | React
 Mathi        | Software Testing | Vallarasu    | Software Testing
 Paari        | Python           | Vijay        | Python & AWS
 Paari        | Spring Boot      | Muthu        | Java & Spring Boot
 Kathir       | Java             | Muthu        | Java & Spring Boot
 Seyon        | React            | Prithvi      | React
(11 rows)

plaintext

Find all students who are learning courses handled by Vallarasu.

cinemas=# select s.student_name
from students s
join student_courses sc
on s.student_id = sc.student_id
join courses c
on sc.course_id = c.course_id
join trainers t
on c.trainer_id = t.trainer_id
where t.trainer_name = 'Vallarasu';

plaintext
o/p:

 student_name 
--------------
 Mathi
(1 row)

plaintext

Find all students who are learning Python, along with their trainer's name.

cinemas=# select s.student_name, t.trainer_name
from students s
join student_courses sc
on s.student_id = sc.student_id
join courses c
on sc.course_id = c.course_id
join trainers t
on c.trainer_id = t.trainer_id
where c.course_name = 'Python';

plaintext
o/p:

 student_name | trainer_name 
--------------+--------------
 Arul         | Vijay
 Paari        | Vijay
(2 rows)

plaintext

Find all students who are learning courses taught by trainers having more than 7 years of experience.

cinemas=# select s.student_name, c.course_name, t.trainer_name
from students s
join student_courses sc
on s.student_id = sc.student_id
join courses c
on sc.course_id = c.course_id
join trainers t
on c.trainer_id = t.trainer_id
where t.experience_years > 7;

plaintext
o/p:

 student_name | course_name | trainer_name 
--------------+-------------+--------------
 Arul         | Python      | Vijay
 Arul         | AWS         | Vijay
 Kavin        | Java        | Muthu
 Venba        | Spring Boot | Muthu
 Paari        | Python      | Vijay
 Paari        | Spring Boot | Muthu
 Kathir       | Java        | Muthu
(7 rows)