DEV Community: R.Shobika CSE

PostgreSQL - AGGREGATE FUNCTION day 3

R.Shobika CSE — Sun, 09 Aug 2026 11:34:03 +0000

** AGGREGATE FUNCTIONS:**

Aggregate function is used to perform the calculation on set input values and return the single value .
Aggregate functions are:
sum,avg,min,max,and count

SUM()

select sum(empsalary) from employee;

MIN()

select min(empsalary) from employee;

MAX()

select max(empsalary) from employee;

AVG()

select avg(empsalary) from employee;

output:

ROUND()

GROUPBY

The GROUP BY clause groups rows that have the same values into summary rows

select emproll ,sum(salary) from employee group by emproll;

output:

PostgreSQL day-2

R.Shobika CSE — Fri, 07 Aug 2026 08:48:35 +0000

CREATE TABLE:

CREATE table student(
stdroll int,
stdname varchar(20),
department varchar(20),
year int);

INSERT :

INSERT INTO students values(01,'shobi','CSE',4),(02,'Nandhini','CSE',4),(03,'Sandra','ECE',2),(05,'Hindhu','EEE',1);

output:

SELECT:

SELECT * from students;

output:

1 . SPECIFICATION SELECTION IN THE TABLE :

SELECT stdname,stddept from students;

output:

ALTER THE TABLE:

ALTER table students rename to std;

output:

SELECT DISTINCT

The SELECT DISTINCT statement is used to return only distinct (different) values.

Inside a table, a column often contains many duplicate values and sometimes you only want to list the different (distinct) values.

SELECT distinct stddept from std;

output:

IF doesnot use the distinct means it will return only selected column values only

WHERE CLAUSE:

The WHERE clause is used to filter records.

SELECT * from std WHERE stddept='CSE';

output:

WHERE and:

WHERE and is same like the other programming language like if both condition true means its execute , if anyone condition false means it execute 0 rows.

SELECT * from student WHERE stddept='ECE' and year=4;

output:

SELECT * from student WHERE stddept='CSE' and year=4;

output:

WHERE or:

WHERE or is also same like other programming language if anyone condition true means it will execute otherwise its execute 0 rows.

SELECT * from student WHERE stdname='shobi' or stddept='ECE';

ouput:

SELECT * from student WHERE stdname='divya' or stddept='AGRI';

output:

AS:

SQL aliases are used to give a table, or a column in a table, a temporary name.

SELECT stddept as department from student;

output:

*WHERE NOT : *

SELECT * from student WHERE stddept <> 'ECE';

or 

SELECT * from student WHERE != stddept='ECE';

or

SELECT * from student WHERE not stddept='ECE';

output:

> GREATER THAN:

SELECT * from student WHERE year>2;

output:

< LESS THAN:

SELECT * from student WHERE year>4;

output:

BETWEEN:

The BETWEEN operator is used to specify the within the range of the given value.

SELECT * from student WHERE stdname BETWEEN 'hindhu' AND ' shobi';

output:

IN :

The IN operator is used to specify the list of possible value .

SELECT * from student WHERE stddept in ('CSE','ECE');

output:

ORDER BY:

Order by is used to sort the values in the database usually order by give the values in ascending order. we can also change it in descending order.

SELECT * from student ORDERBY stdname;

output:

If you want the student name in descending order means you have to give the desc ;

SELECT * from student ORDE BY stdname desc;

output:

LIMIT:

Limit is used to get the limited amount of data like if we want first 5 data means we can give limit 5 then it display the first 5 data.

SELECT stdrollno, stdname from student limit 3;

output:

In Limit we can use the order by keyword

SELECT * from student ORDER BY stddept limit 3;

output:

LIKE :

Like operator is used to get the values in database based on starting letter, ending letter and also inbetween letter

if you want starting letter means 's%';
if you want ending letter means '%s';
if you want inbetween letter means '%a%';

SELECT stdname from student WHERE stdname LIKE '%i';

output:

SELECT stdname from student WHERE stdname LIKE 'h%';

output:

SELECT stdname from stduent where stdname like '%a%';

output:

PostgreSQL day-1

R.Shobika CSE — Thu, 06 Aug 2026 12:02:20 +0000

DBMS:

DBMS stands for "Database Management System"
It is used to manage the data from the database
DBMS is a software is allow to create, update and retrieval of data in a Organized way

RDBMS:

RDBMS stands for "Relational Database Management System"
RDBMS is a program used to maintain relational Database.
The data in RDBMS store in table format . A table is a collection of related entity (entity means things).

SQL:

SQL stands for "Structured Query Language".
SQL lets you access and manipulate databases.

PostgreSQL:

PostgreSQL is a Relational Database Management System
It is a open source RDBMS it is used to store, manage, retrieve and Manipulate the data

Difference between PostgreSQL and MySQL

PostgreSQL	MySQL
More advanced	Beginner friendly
Open Source	Open Source
Large applications	Small & Medium applications
Better performance for complex queries	Faster for simple queries

Installation of PostgreSQL:

1. sudo apt update
2. sudo apt install postgresql postgresql-contrib
3. sudo systemctl status postgresql
4. sudo systemctl enable postgresql
5. sudo -i -u postgres
6.PSQL

comments of PostgreSQL

\h ---> help
\l ---> list
\r ---> stop/recover
\c ---> connect

CREATION OF DATABASE:

CREATE database college;
\c ---> connect the database

*TABLE CREATION *

CREATE table student(
stdroll int,
stdname varchar(20),
department varchar(10),
year int,
);

INSERT DATA INTO A TABLE:

// single value insert
INSERT INTO student values ('01','shobi','CSE',4);

// multiple value insert
INSERT INTO student values ('02','shiva','ECE',3),('03','ajitha','EEE',2);

// we can change the order of the values
INSERT Into student (stdname, stdroll, department, year) values ( 'abi','09','IT',1);

SELECT THE VALUES IN A TABLE

SELECT * from student;

PYTHON-3 DAY -7

R.Shobika CSE — Wed, 05 Aug 2026 14:16:20 +0000

PYTHON TASK

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.

Level 1 :

print(1,2,3,4,5)

Level 2:

student=1
while student<=5:
    print(student)
    student=student+1

output:
1
2
3
4
5

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

Level 1:

print(0,2,4,6,8)

Level 2:

for i in range (0,10,2):
    print(i)

output:
0
2
4
6
8

A newly constructed building has a special lift that does not stop on every floor. For safety reasons, it stops only at every third floor. A person enters the lift at the ground floor and presses the "Up" button. Display the first five floors where the lift will stop.

Level 1:

print(3,6,9,12,15)

Level 2:

floor=3
while floor<=16:
    print(floor)
    floor=floor+3

output:
3
6
9
12
15

A rocket launches with a countdown using only even numbers from 10. Display the countdown.

Level 1:

print(10,8,6,4,2,0)

Level 2:

for i in range(10,-1,-2):
    print(i)

count=10
while count>=0:
    print(count)
    count=count-2

output:
10
8
6
4
2
0

PYTHON DAY-6

R.Shobika CSE — Wed, 05 Aug 2026 13:55:57 +0000

TYPE OF ARGUMENTS:

Positional Arguments
Default Arguments
Keyword Arguments
Variable length Arguments

Positional Arguments:

When we call a function without using a keyword is called positional arguments

def add(num1,num2):
    return num1 + num2
result=add(5,5)
print(result)

output:
10

how to find a one variable type?

we have to find the variable type means by the using the "type"

Syntax

print(type(add))

example:

def add(num1,num2):
     return num1+num2
result=add(10,10)
     print(result)
print(type(add))

output:
100

American Standard Code For Information Interchange

In Python, ASCII (American Standard Code for Information Interchange) refers to a character encoding standard that assigns numeric values from 0 to 127 to 128 specific English characters, digits, punctuation marks, and control codes

What is Modularity?

sentence : Breaking into Pieces/words
segments separate

JSON IN JS

R.Shobika CSE — Tue, 04 Aug 2026 12:49:33 +0000

JSON:

JSON means JavaScript Object Notation.
JSON is a Text Format for storing and exchanging data.
JSON is a array of object.

JSON format:

[ ------------------> ARRAY
{-----------> OBJECT1
----
----
},----------> OBJECT1
{-----------> OBJECT2
----
----
----
}-----------> OBJECT2
]-------------------> ARRAY

API :

API means Application Programming Interface.
It build the communication between frontend and backend.

Fetch:

Fetch is a function we give the parameter as a data URL which means (JSON file)
This function return promise .
If the promise resolve means it will go to the .then function if it is resolve means again it will go to the the next .then function .
If the promise does not resolve means it will go to the .catch function

const api=fetch('https://fakestoreapi.com/products/1')
api.then(()=>console.log("success"))
   .catch(()=>console.log("rejected"))

Output
success

if the URL have some mistake means it will go to .catch block

DISCUSSION AND DOM TASK

R.Shobika CSE — Sat, 01 Aug 2026 12:46:45 +0000

DISCUSSION :

Today we have discuss about hoisting concept:
Hoisting means call the function before the function declaration. Hoisting works only on the function declaration.
In Normal variable declaration if we print the variable without declaration 1st means it give the "reference error or uncaught error"
suppose if we use var datatype for the variable declare after the print statement it give Undefined.

Today DOM Task:

CRUD OPERATION IN DOM:

   <h1 id="helo">welcome</h1>
    <script>
        document.getElementById("helo").remove();
        console.log(name.innerText);
        const create=document.createElement("p");
        create.innerText=" hii everyone !!!!"
        document.body.appendChild(create);
        const create1=document.createElement("h2");
        create1.innerText="bye!!!"
        document.body.appendChild(create1);
        const but = document.createElement("button");
        but.innerText="click me!";
        document.body.appendChild(but);
    </script>

output:

TASK 2:

   <h1 id="hi">HII</h1>
    <h1 id="helo">hello</h1>
    <h2 id="h2"></h2>

    <button  onclick="click1()">click me!!</button>
    <script>
       const hii=document.getElementById("hi")

       const hello=document.getElementById("helo")
       const world=document.getElementById("h2")

       function click1(){
        const new1 = document.getElementById("h2");
        new1.innerText="hello world";
        console.log(new1);
        world.insertBefore(hello,world.children[1])
       }
    </script>

output:

TASK 3:


    <h2 id="one">1</h2>
    <h2 id="two">2</h2>
    <h2 id="three">3</h2>
    <h2 id="four">4</h2>
    <input id="user" type="text">
    <button onclick="del1()">DELETE</button>
    <script>
        const num=document.getElementById("user");
        const array=document.querySelectorAll("h2");
        function del1(){
            const index=Number(num.value)-1;
            if(index>=0 && index<array.length){
                array[index].remove();
            }else{
                const err=document.createElement("p");
                err.innerText="out of Bound";
                document.body.appendChild(err);
            }
        }
    </script>

output:

PYTHON3 DAY-5

R.Shobika CSE — Fri, 31 Jul 2026 12:06:29 +0000

Comparison Operator:

In Python Relation operator is used to compare the two values (<,>,<=,>=,==)

Example:1:

Example:2:

output:

Example:3:

Ternary Operator:

In Ternary operator allow you to assing one value if a condition is true it print a true statement otherwise it print a false statement

Example :

Logical Operator:

Logical operator are used to combine a conditional statement, In python Logical operator has a 3 type
and ---> this operator check when the both side condition has a True it give the output True , if anyone condition is False means it give the output False.
or ----> this operator check the condition if anyone condition True means it give the output as True if both side condition is False means it give False.
not---> Reverses the result, returns False if the result is true

Example:

What is Run time?

Runtime means the time when a computer program is actively running, or the software environment that lets it run
Runtime is when the finished program actually performs its tasks for the user

What is Compile time?

Compile time is the period when a compiler program translates human-readable source code into machine-readable binary code, syntax and semantic checks occur, and compile-time errors are found

What is System Language?

System Language is a 0's and 1's (signals)

Python Input: [TBD]

In Python Input is a function we can get the input from the user

Function

Function is a block of code only run when it is called
Its is used for code repetition

how to define a function?

In python using the def keyword to define a function

def function_name(Parameters):

how to call a function ?

In python we have to call a function in a function name
In Python we can call a function in multiple times

def play():
   print("play a song")
play()

how to return a function?

A Function send back the code to the called them
when function reaches the return statement it stop the executing and send the result back

def cafe(amount):
  print("Amount Paid : ",amount)
  print("order received")
  return "iced americano"
x=cafe(250)
print(x)

Output:
Amount Paid : 250
order received
iced americano

To Be Discussed:

Identity operator
Membership operator
Bitwise operator

PYTHON3 - DAY4

R.Shobika CSE — Thu, 30 Jul 2026 13:29:20 +0000

Conditional Statements:

Conditional Statement is used to control the flow of the execution of the program based on specific condition.

If Statement:

This condition is used to execute the code whether the given condition is true.

mark=90
if mark>=80:
  print("pass")

output:
pass

If-else statement:

This condition is used to execute the code whether the given condition is True otherwise its execute false

age=18
if age>=18:
  print("eligible to vote")
else:
  print("not eligible to vote")

output:
eligible to vote

If-Elif-else statement:

This condition is used to execute the code whether the given condition is true if the given condition false means it goes to the next condition and check the condition is true or not if true means it execute the code otherwise it execute the else part.

a=10
b=20
if a>b:
  print("a is greater")
Elif b>a:
  print("b is greater")
else:
  print("a and b are same")

output:
b is greater

Programming Rules:

Never say "I don't know", say "Let me try"
Known to unknown
Don't think about entire output
think about very next step
Introduce a variable only when it simplifies the solution
Micro to macro
Dry run before you run
Every big problem split three part input, progress, output
Logic first and syntax next

PYTHON3 - DAY3

R.Shobika CSE — Thu, 30 Jul 2026 11:37:58 +0000

Why Java ?

Better Performance
High Security
It Used in Enterprise Application like Banking

To Develop OS
Used for Compiler

C++

To Develop a Game App, Payment Gateway

JavaScript:

JavaScript is a Client side
But Nowdays they change as a server side
Some Company use JS as a Backend in a Midlevel.

*FrameWork *

We doesnot change the architecture it goes with that flow only
For,eg: Django, Springboot

Library

We can change the flow of the architecture.

Python Keyword:

In python the keywords are the reserved words

import keyword
keyword.kwlist

if, elif, else, and, as, True, False, assert,....

SELECTORS

R.Shobika CSE — Thu, 30 Jul 2026 11:18:24 +0000

ELEMENT SELECTORS:

In JavaScript You want to manipulate the HTML you have to find the elements first. There are several ways to do this:

Finding HTML elements by id
Finding HTML elements by tag name
Finding HTML elements by class name
Finding HTML elements by CSS selectors
Finding HTML elements by HTML object collections

Finding HTML elements by id

Its is used to find the HTML element in DOM by using id

<h1 id="name">hello<h1>
<script>
  const ele = document.getElementById("name");
  console.log(ele.innerText);
</script>

output:
hello

Finding HTML elements by tag name

It is used to find HTML element in DOM by Using the Tag name

<h1 id="name">Welcome<h1>
<script>
  const ele = document.getElementByTagName("h1");
  console.log(ele[0].innerText);
</script>

output:
Welcome

Finding HTML elements by class name

It is used to find HTML element in DOM by using the class name

<h1 class="name">shobika<h1>
<script>
  const ele = document.getElementByClassName("name");
  console.log(ele[0].innerText);
</script>

output:
shobika

Finding HTML elements by CSS selectors

Its a Query selector method()

<h1 class="name">JavaScript<h1>
<script>
  const ele = document.querySelector(".name");
  console.log(ele.innerText);
</script>

output:
JavaScript

Finding HTML elements by HTML object collections

Its a querySelectorAll() Method

<h1 class="name">JavaScript<h1>
<h1 class="name">Java<h1>
<script>
  const ele = document.querySelectorAll(".name");
  console.log(ele[1].innerText);
</script>

output:
Java

Task 1: Disabled the button after clicking

    <button id="click" onclick="Clicking()">click me!</button>
    <script>
        function Clicking(){
            const select = document.getElementById("click")
            if(select.disabled==false){
                select.disabled=true;
            }

        }
    </script>

Output:

DOM TASK

R.Shobika CSE — Tue, 28 Jul 2026 11:56:55 +0000

TASK - 1 : LIVE CHARACTER COUNT

    <input id="type" type="text" oninput="show()">
    <p >charater count: <span id="res"></span> </p>
    <script>

        function show(){
           const character= document.getElementById("type");
           console.log(character.value.length)
           const result=document.getElementById("res");
           result.innerText=character.value.length;
            }

output:

In this code I used the oninput event for to get the value of the input . This event is used to track the live count ,searches...

TASK - 2 : PASSWORD SHOW AND HIDE WITH 2 BUTTONS

<input id="pass" type="password">
    <button id="show" onclick="Open()">Show</button>
    <button id="hide" onclick="Close()">hide</button>
    <script>
           const passshow = document.getElementById("pass");
        function Open(){
           if(passshow.type=="password"){
            passshow.type="text";
           } 
        }
        function Close(){
            if(passshow.type=="text"){
                passshow.type="password";
            }
        }
    </script>

output:

TASK -3: PASSWORD SHOW AND HIDE IN SINGLE ICON

 <input id="password" type="password">
    <button id ="eye"  onclick="eyeopen()"><i  class="fa-solid fa-eye"></i></button>


    <script>
        function eyeopen(){
            const Eye=document.getElementById("password");
            if(Eye.type=="password"){
                Eye.type="text";  
                const openeye = document.getElementById("eye")
                openeye.innerHTML = '<i class="fa-solid fa-eye-low-vision"></i>' 
            }
            else{
                Eye.type="password";
                const openeye = document.getElementById("eye")
                openeye.innerHTML='<i  class="fa-solid fa-eye"></i>'
            }
        }
    </script>

output: