DEV Community: boopalan

Data selections

boopalan — Mon, 24 Aug 2026 16:28:37 +0000

Why PostgreSQL is ORDBMS ?

How to now we saw how to create and connect with database, creating tables, today we are going to see more in-depth interactivity with table columns

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

Note do not forget to differentiate each columns by by comma,

\h to helps

\d employee

\d will gives the structure of the table

to insert values in the table first we use the keyword insert, it will trigeres we are going to insert some thing and then we want to define the desigination we are going to insert values in the employee table but but to now we yet not define what we are actually going that desigination, here we want to give all the values for the column.

insert into employee values(123, 'Kavin', 'Software Engineer','DB',25000);

insert into employee values(124, 'Viyan', 'Software Engineer', 'AI',27000);

to verifiy our values are inserted or not

select * form employees

up to now we are actually insert only one values suppose if we want to insert multiple values means how can we able to do it?

TODO

To study more this we can insert values from files directly

does the postgres reads files, then what kind of files it will read, does it reads json, csv
does it reads values form the another database,
dose it reads from the DBMS, RDBMS?

for just now we will see how to insert multiple values in the query

insert into employee values(101, 'Arul', 'Team Lead', 'Front End', 35000), (101, 'Agaran', 'Team Lead', 'DB', 45000);

here we are define more then one row in a single query,

after the values keywords if we use several values seperated by the , it will all takes as the next next rows.

To verify our multiple values inerstion

select * from employees

selecting some columns form the table

select name from employees

select name, designation from employees

select name, dept form employees

suppose if we want to select a name with some conditions means how to it

can we select an name with some conditions this kind of this is where clause, it helps to selection with conditions

suppose if we wan to change the table means how can we able to do it?
Can we able to change the values with the existing values(rows and columns )

yes we can change the table name with vales?

Alter is the keyword helps to change the table name

alter table employee rename to employees;

alter is the keyword we are actually going to change and we are actually specifing what we are actually going to change by using the keyword table and saying which table by the name of the table as employee and finally using the rename keyword is what kind of thing we are to do in the table rename to employees, this rename the tables into employee form employees

different kind of selections

select distinct designation from the employees

the distinct keyword will help to select distinct unique values form the table

but

select designation from the employees

will select all the values in the column

note it is an interview question ?

where clause

it helps to filter the quering the values with more then one conditions

select * from employees where dept = 'DB';

it will select those who all are having the values DB at the dept columns

some of the another examples

select * from employees where designation = 'Team Lead';

suppose of we want to count the queirng result can we able to do it?
Yes for counting the queries we can use count

select count(*) from employees where dept = 'Team Lead';

some of the question are delete , drop and truncate

adding more conditions

using and keyword

select * from employees where dept ='DEV' and designation = 'Manager';

using or keyword

select * from employees where dept = '' or designation = '';

TODO

Redundancy data

primary key
foreign key
candidate key
unique key

TODO

RAID DB

alias

suppose if you want to rename the quering column name, we can do it by using the as

select dept from employees

select dept as  Department from employees

now the dept is renames as the Department

but in the result the Department is converted into lower case

in this way can we able to rename more then one one columns
yes, let we see that

select name as empname, dept as  Department from employees

Not equals to:
!= , <>, not are used for the not equals

select * from employees where dept <> 'DB';

select * from employees where dept != 'DB';

select * from employees where not dept = 'DB';

this three method are used to select not equals

select * from employees where not dept <> 'DB';

between

select * from employees where salary between 19000 and 35000;

does this means can we only able to use it only for the integer ranges?
What are the other data types we can be able to use between ?

select * from employees where not salary between 19000 and 35000;

using in

select * from employees where dept = 'DB' or dept = 'FE';

select * from employees where dept = 'DB' or dept = 'FE' or dept = 'AI';

instead of using check the value one by one can use to check the value in a range of items

select * from employees where dept in ( 'DB', 'FE' , 'AI');

select * from employees where dept not in ( 'DB', 'FE' , 'AI');

what will happen if we change the not in to in not

order by

select * from employees order by dept

postgress basics

boopalan — Sun, 23 Aug 2026 16:41:44 +0000

Today without the decent knowledge in the database we cannot
step in even in a small mini progjects, so companies will expcet
more deper knowlege in the database.
the story of the database begin from the Telephone directory,

Telephone directory

In early day to get some ones phone number we use telephone directory, it helps to find out a right one number what we want form the thousands of numberes, We can idendify number by name, location and with some more additional informations.

Yellow pages

It is helps for to get the business numberes, finding some for our requirement from the thousands of numbere is not easy, we do not who was doing which kind of work, instead of searching the business requirement from the whole telephone directory, we can get the required business numbers from the yellow pages directly

Arrival of personal computers

one of the common thing from this two ways is saving the data in the method of rows and columns. After the development fo the personal computers, we can see the Microsoft excel sheet is the one of the extended version of this feature for personal computer to saving data, micorsoft access is specifically designed for using it as an database.

excel rapidly developed with many features like spreadsheets, formulas, graphs and many more features but one the other hand micorsoft access is developed for only saving and retriving the data faster. it focus the speed and reliability and additional features for the business data storage management systems.

throughout this DBMS we can save data multiple tables, tables and sheets are nearly look like similar, for the business requirement we can create a individual tables for saving the data, instead of saving the whole data in a complex single sheet.

Even though we have use multiple tables, we unable to resolve the relations between the multiple tables, to solve this issue later they move on the RDBMS. it resolve the issue of connecting multiple tables in a single database.

By using the RDBMS we can connect multiple tables, through out this method we can establish the relation ship between the more then one table, helps to track and resolve the business dependencies and complex table structure.

nowadays for development we mostly use the RDBMS.

Some of the RDBMS database are SQLite, MYSQL, Oracle Database and more.

What is SQL?

SQL(structured Query Language) is one of the common term to define the relation ship establishing universal language between the users requirement and the communications between the database. It acts as a standard language to communication, this standard is accepted by many companies and they developed there vendor software to support this SQL.

Where we us the SQLite?

It is light weight and super fast database, we can choose it for the smaller application, most of the android's offline first apps are uses the SQLite database

TODO

log file? need to study more on it, topics like log file reading and more
it is related to big data, relation ship between the data science and ML

what is NOSQL?

it does not use the SQL, it does not store the data in the structured formate, it save the data in the key value pare or in the JSON formate. It is flexible or schema-less

Graph based modes like a location, time based factores we can recommend them suggessions, it acts the nodes and it connect the similer and suggessions for the users to make them sustain more time in there platoform.

Some of the examples for the NOSQL's are MongoDB, Apache Cassendra, Redis, Neo4j and more

which database we want to study?

Based one the busines requirement we can choose the DB. We cannot use the only one DB for all the business requirements, for example bancking anf financila service are mostly depends on the the SQL. social medias, Iot services, real-time analytices are mostly depends on the NOSQL.

At a fresher which DB you want to choose to study, here I am going to study the Postgresql, because it has several advances comparing to the other sql databases.
later we can be able to easily pick NOSQL and most of the other sql database will have similar concepts to the postgres

what is PostgreSQL?

It is Advance Object-Relational DBMS, it has excellent SQL standard and best fo the complex queries and more.

what is the differrence between the POstgres and other databases

History

in the early development Postgresql is called in name of INteractive GRaphics and REsearch. Later they improved it to the next stage with many features and they called it and the POSTGRESQL.

Installation

sudo apt update

it helps to fix the dependenies issues,

sudo apt install postgresql postgresql-contrib

it will install the postgresql database

sudo systemctl status postgresql

to startup on the booting postgresql

sudo systemctl enable postgresql

it will help to enable the postgresql always startup when the computer boots

Who can use Postgres database

sudo -i -u postgres

sudo : is helps we are give the permission for this software as the super user for doing things
-i : is the start a login shell [ Loading the User's Environment automatically ]
-u : is now act as the user

postgres : here postgres is the by default admin user for the postgresql database

here up to now we are just login as in the name of the postgres user name not yet in the database just we are switch by default user to the postgres user

suppose if we want go back we can simple enter the exit for postgres user to the normal user again

NOTE: here anyone can use the postgres database but at now or at the installation we have to use it in the default postgres user

how to use postgres

now we are actually going inside or connecting in to the postgresql database, if we give the psql

normally we can do similar kind of thing like whenever if the give the python in the terminal it will opens the python interpreter

for the security reasons by default other then postgres user database does not allows any one to login in the database.

NOTE: can we change or add another user to login in the database

What is the psql ?

psql is the interactive command-line client for the PostgreSQL server,

some of the helping commands

\h - help

\l - list

\r - stop | recover suppose if we entered an wrong command

name of the database

Owner who is the owner of the database

to quit for the \l
esc → :q

to get all the databases form the postgress ?

\l

here we can ablet to see list of items in the name columns? this all are the default databases in the postgress

we will see about it later in this discussion

how to create a database ?

create database database;

it is insencitieve

CREATE DATABASE DADABASE;

NOTE: whenever if we create or execute a command or query in the database
when have to use ; to define the commend is ending at that point.

CREATE DATABASE movies;

we can able to see all the database name;

suppose or in by mistake if you create a database with wrong name how you will delete the database

DROP DATABASE movies;

finally the database was deleted or removed from out databases

NOTE : it is not recomenede way to remove the do it

How to connect our database?

\C DADABASENAME

\c databasename

it will connect to that particular database what we are looking to connect
when we given as the databasename

To see the version ?

do you think databases have version, just like version in software postgress also have versions, knowing version is importent to moving the development project to the production stage.

to get version of the postgress, we can use

select version();

to esc form version

esc :q

Getting current date using postgress

select curent_data;

it will get the current date for this query

to create a table in the database

what is the minimum requirement to create or ensure it is a table ?

In terms of table prespective, how we can ensure that what we are going to store in the table, for table we are creating it to save some kind of data, without need of saving date we do not need to creating table.

suppose if we try to create a table without defining the
any columns what will happen

DB=# create table TABLE
DB-#

when we just give this line create table TABLE
without semi-colon

you can able to see that in the next line equal(=) sign changes into minus(-),

what was happening in the next line, was - indicate that postgress was actually waiting for your next command for what you will going to given as the next inputs, it will wait for until we ending the line using ;

to end the session just we can simple given the ;

DB=# create table TABLE
DB-#;
SOME ERROR
DB=#

now, you can see an error with invalid sql error

so postgress expect to user to create a at least one column in the table.

we want to define the value type in the columns it will helps to process the data faster and quiceker,
for a business perspective we can not compliment anything in the perforamnce

create table movie(id int);

CHAR(n) - Fixed length text, having limit upto n

VARCHAR(n) - variable length with n limit

TEXT - Unlimited variable length

CHAR (without length) - it will allow as to store only one letter

SMALLINT - small whole numbers ( -32,768 to 32,767 ), we can use it for storing age, and small counts

INTEGER - it allow as to store store values in between -2 to 2 billion

BIGINT - some time integers requires to store more then billion values, in swituations like storing population exeds the count.

DECIMAL(p,s) - some times values need to store in the decimal points

NUMERIC(p,s) - it is similar to the DECIMAL

REAL - Scientific measurements needs Approximate numbers.

DOUBLE PRECISION - Scientific calculations

SERIAL - Auto-incrementing integer

BIGSERIAL - Auto-incrementing big integer

DATE YYYY-MM-DD

TIME HH:MM:SS

TIMESTAMP YYYY-MM-DD HH:MM:SS

TIMESTAMPTZ YYYY-MM-DD HH:MM:SS TZ

INTERVAL 1 year 2 months

TIME WITH TZ HH:MM:SS TZ

BOOLEAN - instead of saving the TRUE, FALSE we can also use as a values NULL

JSON - JSON data

JSONB - Binary JSON

INET - IP address 192.168.1.1

INET - IP network 192.168.1.0/24

MACADDR - MAC address 08:00:2b:01:02:03

POINT - 2D point (x,y)

CIRCLE - Circle <(x,y),r>

BOX - Rectangle (x1,y1),(x2,y2)

anytype[] - Array of typed values

ENUM - helps to store string options in the column
('pending', 'processing', 'shipped', 'delivered')

MONEY - Currency amount

Let we see how to create table inside

can we create tables directly in the postgress ?

just now we saw how to create databases in the postgress but can we create tables in the
postgress, not the strecture of the tables we can only create tables inside database

suppose if we create tables without entering any database, it will show error

ensure that you are inside the database!

movies=#

now we can see that postgres=# is changed movies=#

this indicates we are inside the movies tables

create table movie
(
movie_name varchar(80),
release_data date,
ticket int
);

things we do not want to

create table movie
(
movie_name varchar(80),
release_data date,
ticket int,
);

movie is the name of the table

create table movie here we are going to create a
table using the table keywords

and here we naming table as movie

movie_name, release_data, ticket
this all are the name of the columns and
we define the the value type of the columns

varchar is define we are actually going use string
value is a type for the movie_name column,
as well as we define the colmn type respectively for the release_date, ticket as the type of date and int

suppose if we try to create a table without defining the any columns what will happen

SELECT current_database();

Insert data into the tables

insert into movie values ('syperman', '2021-07-15', '120');

inseting more datas

insert into movie values ('superman', '2022-05-02', '120');

insert into movie values ('flash', '2022-05-02', '120');

here we are actually inserted data in a particular order, what will
happen if we inserted in a wrong formate ?

Suppose if we want to customize the data means how to it?

What will happen if we does not give any one value for this column

can we change the order of the insertion values

insert into movie (release_date, movie_name, ticket) values ( '2024-01-11', 'batman', 120);

insert into movie values ('superman', '2022-05-02', '120');

this type of inerstion is positional arguments

insert into movie (release_date, movie_name, ticket) values ( '2024-01-11', 'batman', 120);

then what is name of this type of insertion

how to select the values for the database tables

getting the values in the tables

* is the universal selector it will get all the values in the table

select * from movie;

select release_date, movie_name, ticket from movie

both methods are equal

* is an universal selector

this kind of questions must be clear only if we practice contineously
update tablename
update table tablenaem

create table name
create tablename

select movie_name, release_date, ticket*4  as family_price from movie;

here the value of the ticket is taken from the table and multiplied by 4 and return then to us, It does not update the values in the table

july 30

boopalan — Thu, 30 Jul 2026 14:54:44 +0000

trying the FFI between the c and the python3

i am planning the do a very simple ffi for an simple c program

int add (int a, int b) {
   return a + b;
}

now let we compile this simple program for the linux

gcc -shared -o libadd.so add.c

using this.so file in python program


import ctypes
import os

if os.name == 'posix':  
    lib = ctypes.CDLL('./libadd.so')
else:  
    lib = ctypes.CDLL('./add.dll')

lib.add.argtypes = [ctypes.c_int, ctypes.c_int]  
lib.add.restype = ctypes.c_int              

result = lib.add(5, 7)
print(f"5 + 7 = {result}")

July 13 blog

boopalan — Sun, 19 Jul 2026 12:43:40 +0000

what is signals in Angular?

https://angular.dev/guide/signals

reading the documentation may like many, but i will not say
that but angular documentation changes my

perspective

we can use many values in signals from primitives to complex
data structures

angular signal is two types

we can use it only for reading the values this type
does not allows us to change the values
and another type is can we can do read and write

signals was either writable or read-only

how to use the signal in the angular

for using signal we have to import in the angular component

import { signal } from '@angular/core';

const count = signal(0);

using them in the javascript

count()

using them in the template

count()

we have two way to change the value signal they are

set() and update()

this two are function we are getting

form the signal

count.set(3);

count.update((value) => value + 1);

changing the values using the angular event binding

// in template
<button (click)="incrementCount()">+1</button>


// in typescript 
count = signal(0);

incrementCount() {
  this.count.update(val => val + 1);
}

we actually saw that signal has read only and writable

now how to convert the writable signal to read only signal

by using asReadonly() function can make a signal

to read only signal, this function actually takes a copy of the
signal and make it as read only values having signal

Computed signals

it is actually read only signal it actually derives its

value from other signals.

suppose if you like to deside the value type for the

signal we can do it by the WritableSignal

import { WritableSignal, signal, Signal } from '@angular/core';

const count: WritableSignal<number> = signal(0);

suppose if you want to use the type for read only signal
we can use the Signal type

const doubleCount: Signal = computed(() => count() * 2);


import { signal, computed } from '@angular/core';

const price = signal(10);

const doublePrice = computed(() => price() * 2);

we know that computed value is read only, and it actually derived

value form the other signal that means if we change the value of

the original signal does that affects the computed signal, yes

actually yes whenever if you change the signal it affects the

computed signal and so it is lazily evaluated.

Note it actually depends the signal value but it does not depends

value of the signal it actually expects the signal changes

effect signal

if you want to track an value and based on the value if you want

to do any action you can use the effect,

if you use any values inside the effect it will be automatically

becomes the dependencies, if you use any signal inside effect. if the

signal changes effect will automatically starts runs

effect(() => {
  console.log(`User set to ${currentUser()} and the counter is ${counter()}`);
});

it is an example form the angular

suppose if you are using the eventlistner, setInterval and setTimeout.

effect((onCleanup) => {
  const timer = setInterval(() => {
    console.log('Tick...');
  }, 1000);

  onCleanup(() => clearInterval(timer)); 
});

july 12 blog

boopalan — Sun, 19 Jul 2026 12:40:33 +0000

july 11 blog

boopalan — Sun, 19 Jul 2026 12:37:09 +0000

Meeting Minutes, July 2026 | ILUGC

Here is the quick recap of what happend in ILUGC Monthly meet, July 11, 2026. Intro Gopi welcomed the participants and gave small introduction about ILUGC Briefed participants about the mailing list Talk 0 Zaid started his talk explaining network fundamentals He explained the physical and hardware layer Discussed MAC, IPV4 and Subnetting He demonstrated concepts using cisco packet tracer

ilugc.in

i am went to chennai to attent the ilugc meet

july 10 blog

boopalan — Sun, 19 Jul 2026 12:35:15 +0000

Update 16 files (354b87ea) · Commits · Boopalan S / TamilEuphonic · GitLab

- /euphonic/stackwords.py - /euphonic/previous.py - /euphonic/utils.py - /euphonic/wordsbetween.py - /euphonic/singleletter.py - /euphonic/partical.py - /euphonic/specificword.py - /euphonic/common.py - /euphonic/__pycache__/previous.cpython-312.pyc - /euphonic/__pycache__/singleletter.cpython-312.pyc - /euphonic/__pycache__/stackwords.cpython-312.pyc - /euphonic/__pycache__/common.cpython-312.pyc - /euphonic/__pycache__/wordsbetween.cpython-312.pyc - /euphonic/__pycache__/specificword.cpython-312.pyc - /euphonic/__pycache__/utils.cpython-312.pyc...

gitlab.com

i am made a drastic changes in this repo

just look the angular docs, what are the things are for angular 17 to 22

https://angular.dev/overview

What is Angular?

Angular is a web framework that empowers
developers to build fast, reliable applications that users love.

it is from the angular docs

July 9 blog

boopalan — Sun, 19 Jul 2026 12:29:12 +0000

DOM
Document Object Model

Before diving into the DOM, we must know the parents, children, siblings tags in the HTML, and a good understanding in the CSS.

In windows document every thing, can can define it with the name root, origin.

Let see what was we are getting in if we try to log the document in javascript

console.log(document)

Is the document an object?
Yes, a document is an object and if we remove the body for the document object the browser window becomes empty.

How to get the body for the document, let we try to get the body from the document object

console.log(document.body)

What are the things we can able to get from the document object

Just like the body, the head is also the sibling to the body, right so we must get something.

console.log(document.head)

need to learn and write more on this topic

July 8 blog

boopalan — Sun, 19 Jul 2026 12:20:16 +0000

As the continuation of the previous libre office impress i am create an animated matrix multiplication there is lot more needed to do in this, but i am happy to share that what i am done today

It seems like we are again going to restructure Tamilrulepy, really it holds a special place in my heart.

So, I am thinking Instead of abandoning of this workflow I am just planning to keep this code alive revisit it in the future,

Some would think giving up a closer one is a bit emotional, but I am eagerly waiting for the new workflow.

My learnings in python

decorator

A simple and easier way to define an instant decorator in python is easy.

If you see in some places developers will use three functions for defining decorator

One interesting thing i get is we can call decorator while using them in the top of the functions

@decorator
@decorator()

Calling a decorator in these two different ways helps to achieve several things.

july 7 blog

boopalan — Thu, 09 Jul 2026 14:43:51 +0000

Grid and flex box

How to move all children tags to center in parent particular tags.

For that we have to first add the display : flex property to the parents

Now if we see all the elements inside the parent tag it will display side by side, Previously it will be vertical one by one.

Default values will be either block or online
Based on the elements perspective

block will for the elements to display
Horizontally one by one.

Online will help to display vertically.

Flex is designed to change the property based on the elements x axis and y axis, can we change and view the elements appearance to we have add the flex property

For better visualization we just add some more height and width for the parent element.

Suppose if we want to change or add some behaviour for the elements in horizontally we want to handle the justify-content property

Let us justify-content property with different values and see how they change.

Flex start

Flex End

Center

Just like horizontal, we will try some of the properties for vertically change, we can use the three values for the same as the align-item.

Flex start

Center

Flex End

Suppose if we use the three properties for this for the parent element it will always be how we described, even if we change the window size, it will remain the same.

What will happen if the window size is less than what we expect,

Let we see what was happening

Was it actually adjusting the width between each element inside the parent tag?

Suppose what will happen if we add more

need to work on more

july 6 blog

boopalan — Thu, 09 Jul 2026 14:24:35 +0000

i am create a ppt in libre office impress

I am forget to take a screenshot with VARUN

Myself I am, Varun meet in Tamilrulepy and just planned how to code most reliable way and most faster way,

Sathya Raj was deeply fascinated by the AI's coding capabilities. I was impressed by his prompt codes. It gives a way to think: is it possible to create a one workflow for getting rules through AI?

Suppose if you are using expo router tabs and if you are developing an app for two kinds of audiences. For example if you want to show a common ui for general users and different ui for the admin’s how can you do it?

I think this could cause a bit of trouble in achieving this one, but based on the database role it might be a simpler one, I need to work on this. If I complete this I will update here.

july 5 blog

boopalan — Sun, 05 Jul 2026 14:42:48 +0000

Great time in the KanchLUG weekly meetup

ideas about some of the projects in the TOSSconf hackathon

idea about where we want to choose the sqlite and postgresql

The de Broglie Hypothesis,Matter Waves and Electron Diffraction,The Double-Slit Experiment
it remembers my schools day and physic class, here he taught in the Physics but It remembers my chemistry classes, my classes books this all are covered my chemistry classes.

I was the maintainer and developer of the tamilstring

I am planning to do at least two releases per year for an year so i am planned a release for this month.

need more contributions

Boopalan S / TamilString · GitLab

GitLab.com

gitlab.com

tamilstring-011d48.gitlab.io