,Chapter 1: What is SQL?
SQL stands for Structured Query Language. It is the language you use to communicate with a
database. Think of a database as a giant, organised collection of tables — just like
spreadsheets in Excel. SQL lets you ask questions like:
• Show me all customers from Varanasi
• What were last month's total sales?
• Add a new student to the records
• Update a person's phone number
SQL is how you do all of these things.
Why should you learn SQL?
• Used by every major company — Amazon, Zomato, banks, hospitals, startups
• Top skill for data analysts, backend developers, and product managers
• Easy to learn — you can write real queries within 2–3 weeks
• Works across many database systems: MySQL, PostgreSQL, SQLite, SQL Server
What does a database look like?
A database contains multiple tables. Each table has rows and columns — just like a
spreadsheet. Here is an example 'students' table:
id name city age marks
1 Aryan Varanasi 20 88
2 Priya Mumbai 22 74
3 Rahul Delhi 21 91
4 Sneha Varanasi 19 67
• Each row = one record (one student)
• Each column = one piece of information (name, city, marks...)
• id = a unique number to identify each row (called a Primary Key)
💡 SQL is NOT case-sensitive. SELECT and select both work. By convention, SQL
keywords are written in UPPERCASE to make them easy to read.
SQL vs Excel — What is the difference?
Feature Excel SQL
Volume of data Struggles with millions of rows Handles billions of rows easily
, Speed Slows down with big files Very fast even on huge datasets
Automation Manual, click-based Write a query once, reuse forever
Multiple tables Limited (VLOOKUP) Joins multiple tables in one query
Used by Individual users Companies, apps, data systems
SQL stands for Structured Query Language. It is the language you use to communicate with a
database. Think of a database as a giant, organised collection of tables — just like
spreadsheets in Excel. SQL lets you ask questions like:
• Show me all customers from Varanasi
• What were last month's total sales?
• Add a new student to the records
• Update a person's phone number
SQL is how you do all of these things.
Why should you learn SQL?
• Used by every major company — Amazon, Zomato, banks, hospitals, startups
• Top skill for data analysts, backend developers, and product managers
• Easy to learn — you can write real queries within 2–3 weeks
• Works across many database systems: MySQL, PostgreSQL, SQLite, SQL Server
What does a database look like?
A database contains multiple tables. Each table has rows and columns — just like a
spreadsheet. Here is an example 'students' table:
id name city age marks
1 Aryan Varanasi 20 88
2 Priya Mumbai 22 74
3 Rahul Delhi 21 91
4 Sneha Varanasi 19 67
• Each row = one record (one student)
• Each column = one piece of information (name, city, marks...)
• id = a unique number to identify each row (called a Primary Key)
💡 SQL is NOT case-sensitive. SELECT and select both work. By convention, SQL
keywords are written in UPPERCASE to make them easy to read.
SQL vs Excel — What is the difference?
Feature Excel SQL
Volume of data Struggles with millions of rows Handles billions of rows easily
, Speed Slows down with big files Very fast even on huge datasets
Automation Manual, click-based Write a query once, reuse forever
Multiple tables Limited (VLOOKUP) Joins multiple tables in one query
Used by Individual users Companies, apps, data systems
