1

INTRO 1

What is SQL?

And why is it one of the most valuable skills you can learn in tech?

3

Learning Blocks

SQL

Interactive Queries

In This Chapter

Concepts you'll master

What a database is and why every app needs one

The difference between a database, a table, a row, and a column

Why SQL has remained the #1 data language for 50+ years

Key terminology you will use throughout your career

Every App you Love Runs on a Database

When you scroll Instagram, the app sends a SQL query that looks something like:

SQL QUERY

SELECT post_id, image_url, caption, like_count 
FROM posts 
WHERE user_id IN (
    Select following_id FROM followers WHERE user_id = ?;
)
ORDER BY created_at DESC
LIMIT 20;

This query runs millions of times per second at scale, SQL is the universal language of data.

💡 Engineering Insight: At Google, databases can have tables with trillions of rows annd schemas with hundreds of tables. Yet the SQL you write today is the same SQL engineers write at Google - the language scales from 8 rows to 8 trillion.