1. What actually is PostgreSQL? (Very honest explanation)
PostgreSQL (most people call it Postgres) is a free & open-source relational database system (RDBMS).
Think of it like a very smart, very organized electronic filing cabinet that:
- Stores huge amounts of structured data
- Keeps everything extremely consistent (thanks to ACID)
- Allows very complex questions (“queries”) to be asked
- Can handle millions of rows and still be fast (if you design it properly)
It is often called the most advanced open-source database in the world.
Quick comparison table (2026 reality):
| Feature | MySQL/MariaDB | PostgreSQL | SQLite |
|---|---|---|---|
| ACID compliance | Yes (with InnoDB) | Full & strict | Yes |
| JSON/JSONB support | Okay | Excellent (best in class) | Basic |
| Advanced indexing | Good | Very advanced (GiST, GIN, BRIN, etc.) | Limited |
| Window functions | Yes | Excellent | Partial |
| Full-text search | Good | Very powerful | Basic |
| Extensibility | Plugins | Write your own functions/types/indexes in C, etc. | Very limited |
| Typical use case 2025–26 | Web apps, WordPress | Complex apps, GIS, analytics, fintech | Mobile/local apps |
So PostgreSQL = power + reliability + future-proof
2. Very first things — Let’s create our playground
Most common ways in 2026:
- Local install → PostgreSQL 17 or 18 + pgAdmin 4 or DBeaver
- Docker (very popular now): docker run -d -p 5432:5432 -e POSTGRES_PASSWORD=mysecretpassword postgres:18
- Free cloud → Neon.tech, Supabase, Fly.io Postgres, Render, Railway, ElephantSQL, etc.
For learning today → let’s pretend we already have PostgreSQL running locally and we can use either:
- psql (command line)
- pgAdmin (GUI)
- DBeaver (modern favorite)
3. Step-by-step PostgreSQL class — like school
Lesson 1: Create your first database
SQL
|
0 1 2 3 4 5 6 7 8 9 10 |
-- In psql or any client CREATE DATABASE school_db; -- Connect to it (in psql) \c school_db |
Lesson 2: Create our first table — Students
SQL
|
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 |
CREATE TABLE students ( id BIGSERIAL PRIMARY KEY, -- auto-incrementing number first_name VARCHAR(50) NOT NULL, last_name VARCHAR(50) NOT NULL, email VARCHAR(100) UNIQUE NOT NULL, date_of_birth DATE, is_active BOOLEAN DEFAULT TRUE, gpa NUMERIC(3,2), -- like 8.75 created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP ); |
BIGSERIAL = best auto-increment type in modern Postgres
Lesson 3: Insert some real-looking data
SQL
|
0 1 2 3 4 5 6 7 8 9 10 |
INSERT INTO students (first_name, last_name, email, date_of_birth, gpa) VALUES ('Rahul', 'Sharma', 'rahul.sharma.2003@gmail.com', '2003-07-14', 8.9), ('Priya', 'Verma', 'priya.verma22@yahoo.com', '2002-11-03', 9.1), ('Aarav', 'Patel', 'aarav.patel@outlook.com', '2004-02-28', 7.8), ('Sneha', 'Reddy', 'sneha.reddy06@gmail.com', '2003-05-19', 8.4); |
Lesson 4: Basic SELECT — most important command
SQL
|
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 |
-- All students SELECT * FROM students; -- Only names and GPA SELECT first_name, last_name, gpa FROM students; -- Students with GPA > 8.5 SELECT first_name, last_name, gpa FROM students WHERE gpa > 8.5; -- Sort by GPA descending SELECT first_name, last_name, gpa FROM students ORDER BY gpa DESC; |
Lesson 5: Update and Delete (be careful!)
SQL
|
0 1 2 3 4 5 6 7 8 9 10 11 12 13 |
-- Aarav improved! UPDATE students SET gpa = 8.6, is_active = TRUE WHERE email = 'aarav.patel@outlook.com'; -- Delete inactive students (none right now) DELETE FROM students WHERE is_active = FALSE; |
Lesson 6: Very important → Relationships (Foreign Keys)
Let’s create a courses and enrollments table.
SQL
|
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 |
CREATE TABLE courses ( id BIGSERIAL PRIMARY KEY, code VARCHAR(10) UNIQUE NOT NULL, -- like CSE101 name VARCHAR(100) NOT NULL, credits SMALLINT DEFAULT 4 ); CREATE TABLE enrollments ( id BIGSERIAL PRIMARY KEY, student_id BIGINT REFERENCES students(id) ON DELETE CASCADE, course_id BIGINT REFERENCES courses(id) ON DELETE CASCADE, grade CHAR(1), -- A,B,C,D,F enrolled_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP, CONSTRAINT one_enrollment_per_course UNIQUE(student_id, course_id) ); |
Now insert:
SQL
|
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 |
INSERT INTO courses (code, name, credits) VALUES ('CS101', 'Introduction to Programming', 4), ('DBMS01', 'Database Management Systems', 4), ('ML101', 'Machine Learning Basics', 3); INSERT INTO enrollments (student_id, course_id, grade) VALUES (1, 1, 'A'), -- Rahul - Programming (1, 2, 'A+'), -- Rahul - DBMS (2, 1, 'B+'), -- Priya - Programming (3, 3, 'B'); -- Aarav - ML |
Lesson 7: JOIN — the real power of relational databases
SQL
|
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 |
-- Which students are enrolled in which courses? SELECT s.first_name || ' ' || s.last_name AS student_name, c.name AS course_name, e.grade FROM students s JOIN enrollments e ON s.id = e.student_id JOIN courses c ON c.id = e.course_id ORDER BY student_name, course_name; |
Expected output:
text
|
0 1 2 3 4 5 6 7 8 9 10 11 |
student_name | course_name | grade -----------------|------------------------------------|------ Aarav Patel | Machine Learning Basics | B Priya Verma | Introduction to Programming | B+ Rahul Sharma | Database Management Systems | A+ Rahul Sharma | Introduction to Programming | A |
Quick Summary — What we learned today
| Concept | Command/Example | Why important? |
|---|---|---|
| Create database | CREATE DATABASE shop | Your container |
| Create table | CREATE TABLE products (…) | Structure of data |
| Insert | INSERT INTO … VALUES … | Put data inside |
| Select + Where | SELECT … WHERE gpa >= 8.0 | Ask questions |
| Update / Delete | UPDATE … SET … WHERE … | Change / remove records |
| Foreign key | REFERENCES students(id) | Connect tables |
| JOIN | JOIN table ON table.id = other.id | Combine information from many tables |
Your first homework (try this!)
- Create one more table called teachers
- Add 2–3 teachers
- Create teaches table (relation between teachers & courses)
- Write a query that shows: Student name → Course name → Teacher name → Grade
Want to continue?
Tell me:
- You want to go deeper into JOINs (LEFT, RIGHT, FULL)?
- Aggregations (COUNT, AVG, GROUP BY)?
- JSONB (super powerful in 2026)?
- How to install on your laptop?
- Indexing & performance?
Just say the next topic — I’m here like your 24/7 Postgres guru! 🚀
