Category: SQL

Up until now, we’ve been working with one table at a time. But in real life, data is almost always spread across multiple tables (customers in one table, orders in another, products in a...

A subquery (also called a nested query) is simply a SELECT statement inside another SELECT statement. It’s like asking a question, and inside the answer you ask another smaller question. Subqueries make SQL incredibly...

Set operations let you combine the results of two or more SELECT queries as if they were mathematical sets. Think of each SELECT as producing a “bag of rows”. With set operations, you can:...

Up until now, we’ve been creating tables, inserting data, and reading it with SELECT. But real databases are alive — prices change, stock gets updated, customers cancel orders, old records get archived… That’s what...

This is where we go beyond just reading and writing data and start transforming it like real data ninjas! In real life, raw data from the database is often ugly or incomplete: Prices without...

A VIEW is like a saved query that you can treat almost exactly like a real table. You write a complex SELECT once, give it a name, and then you can query that view...

This is the chapter where we learn how to turn a slow, crawling database into a super-fast, responsive one! Imagine your books table has 1 million rows. You run this query: SQL

Without...

This is where SQL becomes almost like a real programming language! Up until now, we’ve been writing queries directly every time we need something. But in real-world applications (especially big systems like e-commerce, banking,...

One of the most important theoretical chapters in the entire SQL course! Database Normalization is the process of organizing data in a database to reduce redundancy (duplicate data) and prevent data anomalies (problems when...

The grand finale of our SQL journey! By now you’re already writing solid, production-ready queries. This chapter is where we go pro-level: features that make analysts, data engineers, and backend developers say “wow, that’s...