DEV Community: Ezhil Abinaya K

Postgresql Operators

Ezhil Abinaya K — Wed, 12 Aug 2026 14:44:25 +0000

Greater Than
The > operator is used when you want to return all records where a columns is greater than a specified value.

SELECT * FROM cars
WHERE year > 1975;

Less Than or Equal To
The <= operator is used when you want to return all records where a column is less than, or equal to, a specified value.

SELECT * FROM cars
WHERE year <= 1975;

Greater Than or Equal to
The >= operator is used when you want to return all records where a columns is greater than, or equal to, a specified value.

SELECT * FROM cars
WHERE year >= 1975;

LIKE
The LIKE operator is used when you want to return all records where a column is equal to a specified pattern.The pattern can be an absolute value like 'Volvo', or with a wildcard that has a special meaning.
There are two wildcards often used in conjunction with the LIKE operator:

The percent sign %, represents zero, one, or multiple characters.
The underscore sign _, represents one single character. Return all records where the model STARTS with a capital 'M':

SELECT * FROM cars
WHERE model LIKE 'M%';

Reference
https://www.w3schools.com/postgresql/postgresql_operators.php

Select Query

Ezhil Abinaya K — Tue, 11 Aug 2026 13:56:07 +0000

Select Data
To retrieve data from a data base, we use the SELECT statement.
Specify Columns
By specifying the column names, we can choose which columns to select:

SELECT brand, year FROM cars;

Return ALL Columns
Specify a * instead of the column names to select all columns:

SELECT * FROM cars;

Display Table
To check the result we can display the table with this SQL statement:

SELECT * FROM cars;

PostgreSQL Operators
Greater Than
The > operator is used when you want to return all records where a columns is greater than a specified value.
Return all records where the year is greater than 1975:

SELECT * FROM cars
WHERE year > 1975;

Less Than or Equal To
The <= operator is used when you want to return all records where a column is less than, or equal to, a specified value.
Return all records where the year is less than or equal to 1975:

SELECT * FROM cars
WHERE year <= 1975;

Reference
https://www.w3schools.com/postgresql/postgresql_operators.php

PostgreSQL

Ezhil Abinaya K — Fri, 07 Aug 2026 14:13:56 +0000

PostgreSQL
PostgreSQL is a free open-source database system that supports both relational (SQL) and non-relational (JSON) queries.PostgreSQL is a back-end database for dynamic websites and web applications.In first postgreSQL name is Ingres --> Interactive Graphics and Research.
Installation

sudoapt update

It is a command used in linux to install, update and mange software packages.sudo means superuser do, i.e., running a command with admin rights. apt means advanced package tool like playstore.

sudo apt install postgresql postgresql - contrib

Check if postgreSQL is successfully installed. Open terminal then run these commands.

sudo -i -u postgres

i means login shell, u means user.
\h means help
\l means list the database
\r means stop
Esc-shift-:q means quit
\c means connect
To see the postgres version

select version();

select current-date;

create table employee(empid integer,name varchar(25),designation varchar(25),dept varchar(25),salary integer();

insert into employee values (123,'vasan','software developer','db',25000);
insert into employee values (124,'aadhi','software developer','AI',27000);

select * from employee;

DATABASE

Ezhil Abinaya K — Thu, 06 Aug 2026 13:53:54 +0000

Database
Data refers to raw, unorganized facts and figures that can be processed to generate meaningful information. A database is a structured system used to store, manage, and retrieve data efficiently for multiple users and applications.
Types of database
1.Relational Database - stores data in tables
(Eg)MySQL, PostgreSQL, Oracle, Microsoft SQL Server.
2.NoSQL(Not Only SQL) Database - unstructured data
Document Databases – Store data as JSON-like documents. (Example: MongoDB)
Key-Value Stores – Store simple key–value pairs for fast lookups. (Example: Redis)
Columnar Databases – Store data by columns for analytics. (Example: Apache Cassandra)
Graph Databases – Store nodes & relationships for connected data. (Example: Neo4j)
3.Object-Oriented Database - object storage
4.Hierarchical Database -tree like structure
Working of Databases
Databases work by organizing and storing information in a structured or unstructured format, allowing easy access, retrieval, and modification. At the core of every database system is the Database Management System (DBMS)- a software layer that acts as an intermediary between users and the raw data.
Reference
https://www.geeksforgeeks.org/dbms/what-is-database/

Python Tasks

Ezhil Abinaya K — Wed, 05 Aug 2026 14:42:15 +0000

1.Five students enter the classroom one after another. The first student gets roll number 1, the second gets 2, and so on. Display the assigned roll numbers.

2.A coach asks students to stand only at even-numbered positions in a queue. Display the first five positions.

Python Module

Ezhil Abinaya K — Tue, 04 Aug 2026 12:30:27 +0000

Python Modules
Module is a file containing definitions and statements. A module can define functions, classes and variables. Modules help organize code into separate files so that programs become easier to maintain and reuse. Instead of writing everything in one place, related functionality can be grouped into its own module and imported whenever needed.
Create a Module
To create a module, write the desired code and save that in a file with .py extension.
Example: Let's create a function_demo.py in which we define four functions, one add,one sub,one mul and one div.

def add(a,b):
    return a+b
def sub(a,b):
    return a-b
def mul(a,b):
    return a*b
def div(a,b)
    return a//b
developer ="Ezhil"

This is all that is required to create a module.
Import module
Modules can be used in another file using the import statement. When Python sees an import, it loads the module if it exists in the interpreter’s search path. Below is the syntax to import a module:

import module

Example: Here, we are importing the function_demo.py that we created earlier.

import function_demo
result=function_demo.add(100,150)
print(result)
//250

Python is a dynamically typed programming language.
Reference
https://www.geeksforgeeks.org/python/python-modules/

useNavigate()

Ezhil Abinaya K — Mon, 03 Aug 2026 15:00:50 +0000

useNavigate()
useNavigate() is a hook provided by React Router.

It allows us to navigate from one route to another using JavaScript.

For example, imagine we have:

/home
/about
/contact
If I want to move to /about when a button is clicked, I can use useNavigate().

import { useNavigate } from "react-router-dom";

function Home() {
  const navigate = useNavigate();

  return (
    <button onClick={() => navigate("/about")}>
      Go to About
    </button>
  );
}
export default Home;

Why do we need useNavigate()?

This was the part that helped me understand it better.Sometimes navigation should happen after some action.
For example:
After login → go to Dashboard
After form submission → go to Success page
After logout → go to Login page
After completing a quiz → go to Result page
In these situations, we don't just want a normal link.We want navigation to happen based on some logic.
That's where useNavigate() becomes useful.
Here,
const navigate = useNavigate();gives us a navigate function.
Then navigate("/about");means “Go to the /about route.”

BrowserRouter in React

Ezhil Abinaya K — Sun, 02 Aug 2026 14:09:12 +0000

BrowserRouter
BrowserRouter is a component provided by React Router to enable client-side routing using the HTML5 history API, allowing navigation without full page reloads. It also updates the browser URL dynamically while preserving the application state during view changes.
Syntax

<BrowserRouter>
      <Routes>
        <Route path="/" element={<Home />} />
        <Route path="/about" element={<About />} />
      </Routes>
</BrowserRouter>

Install React Router
In the command line, navigate to your project directory and run the following command to install the package:

npm install react-router-dom

Wrap Your App with BrowserRouter

function App() {
  return (
    <BrowserRouter>
      {/* Your app content */}
    </BrowserRouter>
  );
}

Basic Routing
React Router uses three main components for basic routing:

Link: Creates navigation links that update the URL
Routes: A container for all your route definitions
Route: Defines a mapping between a URL path and a component

import { BrowserRouter, Routes, Route, Link } from 'react-router-dom';

function Home() {
  return <h1>Home Page</h1>;
}

function About() {
  return <h1>About Page</h1>;
}

function Contact() {
  return <h1>Contact Page</h1>;
}

function App() {
  return (
    <BrowserRouter>
      {/* Navigation */}
      <nav>
        <Link to="/">Home</Link> |{" "}
        <Link to="/about">About</Link> |{" "}
        <Link to="/contact">Contact</Link>
      </nav>

      {/* Routes */}
      <Routes>
        <Route path="/" element={<Home />} />
        <Route path="/about" element={<About />} />
        <Route path="/contact" element={<Contact />} />
      </Routes>
    </BrowserRouter>
  );
}

BrowserRouter wraps your app and enables routing functionality
Link components create navigation links
Routes and Route define your routing configuration

References

Using def Function Practice Programs in Python

Ezhil Abinaya K — Sat, 01 Aug 2026 15:24:56 +0000

def painter():
    print("painting")


painter()
//
painting

2) Create a function called add(),sub(), and get the input for a and b inside every function then print the result.

def add():
    a=int(input("enter a"))
    b=int(input("enter b"))
    print(a+b)
    print("ok")

add()
//
enter a 10
enter b 20
30
ok

def sub():
    print("subtraction")
    a=int(input("enter a"))
    b=int(input("enter b"))
    print(a-b)


sub()
//
subtraction
enter a 30
enter b 20
10

3) Get a integer number from user and pass it to the function called findevenorodd().Let the function print whether the number is even or odd.

def findevenorodd(a):
    if (a%2==0):
        print("even")
    else:
        print("odd")


findevenorodd(10)
even

def Keyword in Python

Ezhil Abinaya K — Fri, 31 Jul 2026 15:00:42 +0000

Python def Keyword
def keyword is used to define user-defined functions. Functions help organize code into reusable blocks, making programs easier to read, maintain, and reuse. They can accept input values through parameters, perform specific tasks and optionally return results.

def func():
    print("Hello")

func()
//Hello

Syntax

def function_name(parameters):
    # Code to execute
    return value  # Optional

function_name: Name of the function.
parameters (optional): input values passed to the function.
return (optional): statement used to send a value back to the caller.

def is a keyword for defining function in python ? True
Function should always return any value?False
Function should always have parameters?False

Error handled in Python till now is:
Indentation Error
Type Error
Syntax Error
Name error
Positional Arguments
Positional arguments mean values are passed in the same order as parameters are defined in the function.The first value goes to the first parameter, second to the second and so on.Changing the order can lead to unexpected results.

def add(a, b):
    return a + b

# 5 goes to a, 10 goes to b
print(add(5, 10))
//15

Reference
http://geeksforgeeks.org/python/python-def-keyword/

If,elif,else Statements and Practice Programs in Python

Ezhil Abinaya K — Thu, 30 Jul 2026 08:40:53 +0000

Conditional Statements in Python
Conditional statements are used to control the flow of execution in a program based on specific conditions. They allow programs to execute different blocks of code depending on whether a condition evaluates to True or False.
If Statement
If statement is used to execute a block of code only when a specified condition evaluates to True.

age = 20
if age >= 18:
    print("Eligible to vote.")
//Eligible to vote.

Short Hand if
Short-hand if is used to write if statements in a single line. It is useful when only one statement needs to be executed.

age = 20
if age >= 18:print("Eligible to vote.")
//Eligible to vote.

In other language the if statement condition must inside the parentheses. but,in python there is no necessary need to put the parentheses for if().We write if condition or if(condition) also.

mark1=90
mark2=96;
if mark1>mark2:
    print("mark1 is greater")
elif mark2>mark1:
    print("mark2 is greater")
else:
    print("both are equal")
//   
mark2 is greater

elif is nothing it is same as else if . In python we use elif.
Additional Information
In your free time, read the "zen of python".It is a collection guiding principles.
Programs

Write a Program to display the last digit of a number. 2.Write a Program to check if a single character is a vowel or not. Take the character as input from the user.(TBD)

ch = input('Enter a single character: ')
Enter a single character: i
if ch.lower() in "aeiou":
    print("It is Vowel")
else:
    print("It is not a vowel")
//   
It is Vowel

3.Write a Program to check if a number is even or odd where number is taken as input.

num = int(input("Enter a number"))
Enter a number1
if num % 2 == 0:
    print("Given number is even")
else:
    print("Given number is odd")
//
 Given number is odd

4.Write a Program to check if 3rd last character of a string is a vowel or not.(TBD)

word = input("Enter a word")
if len(word)<=2:
    print("Given word is too small")
else:
    char = word[-3]
    if char.lower() in "aeiou":
        print("It is a Vowel")
    else:
        print("Not a vowel")

5.Check if the first and last number of a list is same or not.

l = [1, 2, 3, 46, 9, 2, 1, 5, 5]
if l[0] == l[-1]:
    print("First and Last number is same")
else:
    print("They are not same")
//
They are not same

6.Calculate income tax for the input income by adhering to the Indian rules.(TBD)
there is no tax on income till Rs. 250000,
5% on between Rs. 250001 to Rs. 500000,
10% on between Rs. 500001 to Rs. 1000000,
20% on between Rs. 1000001 to Rs. 2000000,
30% on between Rs. 2000001 to Rs. 3000000,
40% on above Rs. 3000001

income = int(input("Enter your income"))
if income <= 250000:
    total_tax = 0
elif income>250000 and income<=500000:
    taxableincome = income-250000
    total_tax = taxableincome*0.05
elif income>=500001 and income<=1000000:
    taxableincome = income-500000
    tax1=(taxableincome/100)*10
    total_tax= tax1+12500
elif income>=1000001 and income<=2000000:
    taxableincome = income-1000000
    tax1=(taxableincome/100)*20
    total_tax= tax1+12500+50000
elif income>=2000001 and income<=3000000:
    taxableincome = income-2000000
    tax1=(taxableincome/100)*30
    total_tax= tax1+12500+50000+200000
elif income>=3000001 :
    taxableincome = income-3000000
    tax1=(taxableincome/100)*40
    total_tax= tax1+12500+50000+200000+300000
print("Payable tax: ", total_tax)

7.Write a Program to calculate percentage of a student through 5 subjects. Take marks as input from the user.
Using percentage print which grade the student has scored.

m = int(input("Enter number for maths: "))
Enter number for maths: 100
p = int(input("Enter number for phy: "))
Enter number for phy: 80
c = int(input("Enter number for chem: "))
Enter number for chem: 80
b = int(input("Enter number for bio: "))
Enter number for bio: 79
e = int(input("Enter number for eng: "))
Enter number for eng: 89
sub_marks = m + p + c + b + e
total_mark=int(input("Enter Maximum marks"))
Enter Maximum marks400
perc = (sub_marks/total_mark)*100
if perc>90:
    print("You have got A+ Grade")
elif perc<=90 and perc>80:
    print("You have got A Grade")
elif perc<=80 and perc>70:
    print("You have got B+ Grade")
elif perc<=70 and perc>60:
    print("You have got B Grade")
elif perc<=60 and perc>50:
    print("You have got C+ Grade")
elif perc<=50 and perc>40:
    print("You have got C Grade")
elif perc<=40 and perc>33:
    print("You have got D Grade")
else:
    print("You are Fail")

 //
You have got A+ Grade

8.Write a Program to print the day based on the number input.

d = {1:"Monday", 2:"Tuesday", 3:"Wednesday",4:"Thrusday", 5:"Friday", 6:"Saturday", 7:"Sunday"}
num=int(input("Enter a number"))
Enter a number: 7
if num<7 and num>=1:
    print(d[num])
else:
    print("Invalid Number")
//    
Invalid Number

References
https://www.geeksforgeeks.org/python/conditional-statements-in-python/
https://edslash.com/if-else-practice-questions-in-python/

Keywords and Data Types in Python

Ezhil Abinaya K — Wed, 29 Jul 2026 14:01:42 +0000

Keywords
Python has a set of keywords that are reserved words that cannot be used as variable names, function names, or any other identifiers.There are 35 keywords. How to know the keywords list.To see the complete list of reserved words in python in the following:

import keyword 
keyword.kwlist
['False', 'None', 'True', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']
len(keyword.kwlist)
35

Data Types
Variables can store data of different types, and different types can do different things.Python has the following data types built-in by default, in these categories:
Numeric Types: int, float, complex
Sequence Types: list, tuple, range
Mapping Type: dict
Set Types: set, frozenset
Boolean Type: bool
Binary Types: bytes, bytearray, memoryview
None Type: NoneType
Apart from python additional information to be known:

In a website, the side where the user can view the content and perform any action is known as the client side. The server side or backend, refers to the area hidden from users and in charge of storing and browsing data.
There are different kinds of text editors around the world, some of them are vim,emacs,vi,. These are called Terminal based text editors.
notepad,notepad++,sublime text, Ms-word,libreoffice writer.These are called Graphical user interface editors.
Is there any tamil programming language published?Yes there are few.The first open source tamil programming lanugage is Ezhil(எழில்).It was created by Muthiah Annamalai.It was officially anounced in july 2009.It was developed using python.

References
https://www.w3schools.com/python/python_ref_keywords.asp
https://www.w3schools.com/python/python_datatypes.asp
https://codeinstitute.net/global/blog/client-side-vs-server-side/