Learn�SQL�Introduction

Lesson 01 � Foundation

SQL SE
DATA SE BAAT KARO.

Har company, har app, har website � sab ke peeche ek database hai. SQL woh language hai jisse aap us database se sawaal karte ho. Data analyst ke liye SQL seekhna optional nahi, mandatory hai.

? 15 min✓ Beginner✓ No prerequisite

WHY: SQL kyun?

Jab aapko kisi company ke data mein se kuch samajhna ho � sales kitne hain, kaunse product zyada bik raha hai, customer kya chahte hain � tab aapko database se data nikalna padta hai. SQL us data tak pahunchne ka sabse seedha raasta hai.

DATABASE

Data ka organized collection. Jaise ek almirah jismein sab cheezein properly rakhi hain � bank records, student data, product inventory � sab ek database mein hota hai.

TABLE

Database ke andar data row-column format mein hota hai. Jaise Excel sheet � har row ek record hai, har column ek field (name, age, marks).

QUERY

Data se sawaal puchna. "Mujhe sab students ka naam chahiye jinke marks 80 se zyada hain" � yeh ek SQL query hai.

HOW: pehla database banao

Sabse pehle ek database create karte hain, usmein table banate hain, aur data daalte hain. Yeh SQL ki basic flow hai: CREATE ✓ INSERT ✓ SELECT.

sql
-- Database banao
CREATE DATABASE dswallah;
USE dswallah;

-- Table banao
CREATE TABLE students (
 id INT PRIMARY KEY,
 name VARCHAR(100),
 age INT,
 course VARCHAR(50),
 marks DECIMAL(5,2)
);

-- Data daalo
INSERT INTO students VALUES
(1, 'Aman', 22, 'Data Science', 85.50),
(2, 'Priya', 21, 'Python', 92.00),
(3, 'Rahul', 23, 'SQL', 78.50);

-- Data dekho
SELECT * FROM students;
ℹ
Mental model: Database ek folder hai, table ek file hai, aur queries us file se data nikalne ke tareeke. Jaise SELECT * matlab "saari rows dikhao".

Try it: SQL query likho

Neeche ka editor SQL jaisa hai. Yahan apni query likho aur "Run Query" dabao. Screen par sample results dikhenge � yeh browser-based simulation hai, real database nahi.

SQL playgroundSample data se results dikhenge
Run Query dabayein
Simulated execution � sample dataset

SQL syntax ke basics

SQL mein har statement semicolon (;) se end hota hai. Keywords ko uppercase mein likhna convention hai (Python jaise compulsory nahi). Comments -- se lagte hain.

sql
-- Yeh ek comment hai
SELECT name, marks FROM students WHERE marks > 80;

-- Multiple columns lo
SELECT name, course, marks FROM students;

SQL ka basic flow

1. DATABASE BANAO

CREATE DATABASE � naya database banao ya USE karo existing ko.

2. TABLE BANAO

CREATE TABLE � columns define karo: kaunsa data kaisa aayega (INT, VARCHAR, etc.).

3. DATA DAALO

INSERT INTO � rows add karo table mein.

4. QUERY KARO

SELECT � data nikalo aur analysis karo.

Quick check

Ek CREATE TABLE statement likho jo ek courses table banaye with columns: id (INT), name (VARCHAR), duration (VARCHAR).

CREATE TABLE se shuru karo, column names aur types likho, aur PRIMARY KEY bhoolna mat.

Common beginner mistakes

SQL ka introduction complete?

Ab SELECT statement par chalo � taaki data ko filter, sort aur explore kar sako.