SQL & Databases

What is a database, really?

Why we don't just save everything in a text file, and the one idea every database in the world is built on.

The relational model - tables, rows and columns

Why almost every serious database organizes data into tables, and the set theory quietly sitting underneath them.

Data types and NULL: what a column is allowed to hold

Why databases force every column to have a fixed type, and the surprisingly tricky logic of "missing" data.

Setting up your first database

Installing a real database on your machine, connecting to it, and running your very first commands - the practical, hands-on lesson.

Database Foundations Quiz

8 questions

DDL: defining the structure of your data

CREATE, ALTER and DROP - the SQL commands that build and change the shape of your database, plus every constraint that keeps data honest.

DML: inserting, updating and deleting rows

INSERT, UPDATE and DELETE in depth, plus why every one of them should almost always be wrapped in a transaction.

SELECT: reading data the way you'll do it most

The anatomy of a SELECT statement, the order it actually executes in, sorting, and paging through results.

Filtering and pattern matching text

LIKE, wildcards, regular expressions, and why searching text inside a database is a different problem from searching numbers.

Set operations and built-in functions

UNION, INTERSECT and EXCEPT for combining query results, plus the string, date and NULL-handling functions you'll use in nearly every real query.

SQL Fundamentals Quiz

10 questions

Joins: the set theory behind combining tables

INNER, LEFT, RIGHT and FULL joins explained with Venn diagrams, foreign keys, and the Cartesian product they're all built from.

Aggregate functions and GROUP BY

COUNT, SUM, AVG, MIN, MAX, and how GROUP BY turns rows into summarized buckets - plus why HAVING exists and WHERE can't do its job.

Subqueries and CTEs - thinking in multiple steps

Nesting queries inside queries, and using WITH clauses to name and reuse intermediate results cleanly.

Window functions - per-row analytics without collapsing rows

RANK, ROW_NUMBER, running totals, and the OVER clause - the advanced tool that GROUP BY structurally cannot do.

Self-joins, EXISTS, and conditional aggregation

Joining a table to itself, the EXISTS/NOT EXISTS pattern, the NOT IN NULL trap, and pivoting rows into columns with CASE.

Joins & Aggregation Quiz

11 questions

ER modeling: designing tables before you build them

Entities, attributes, and relationships - how to go from a real-world idea to a set of tables, on paper, before writing any SQL.

Functional dependencies and normalization (1NF-3NF)

The precise, mathematical reason certain table designs cause update anomalies, and the normal forms that systematically fix them.

Indexes: how databases actually find things fast

The B-tree explained from scratch, why it gives O(log n) lookups, and when adding an index makes things worse, not better.

Constraints and data integrity in depth

Foreign key actions (CASCADE, RESTRICT, SET NULL), CHECK constraints revisited, and referential integrity as the schema's immune system.

Design & Normalization Quiz

9 questions

ACID and transactions: the four promises every database makes

What a transaction actually is, and the precise meaning of Atomicity, Consistency, Isolation and Durability.

Concurrency and isolation levels

Dirty reads, non-repeatable reads and phantom reads explained one at a time, and the four isolation levels that prevent (or allow) each.

Query execution and EXPLAIN: seeing what the database actually does

How a SQL query becomes a physical execution plan, reading EXPLAIN output, and the join algorithms the planner picks between.

Performance tuning, hands-on: fixing a genuinely slow query

A real slow query, diagnosed and fixed step by step using EXPLAIN, indexing, and query rewriting - tying the whole module together.

Transactions & Performance Quiz

8 questions

What is PostgreSQL, and why does it exist?

The history and philosophy behind PostgreSQL, and why it's become the default choice for so many new projects.

Installing and setting up PostgreSQL properly

A real, thorough PostgreSQL setup: installation, roles and permissions, psql, and connecting from application code.

PostgreSQL-specific features that set it apart

JSONB, arrays, full-text search, and PostGIS - the features that go beyond the standard SQL covered so far in this course.

PostgreSQL in the cloud vs self-hosted: making the real decision

Managed cloud Postgres vs running it yourself - the actual trade-offs in cost, control, and operational burden, with real provider names.

PostgreSQL Deep Dive Quiz

7 questions

What is MySQL, and why does it exist?

The history of MySQL, its relationship to MariaDB, and why it became the database behind most of the early web.

MySQL storage engines and setup

Installing MySQL/MariaDB, InnoDB vs MyISAM in depth, and the mysql command-line client.

MySQL vs PostgreSQL: an honest, practical comparison

Where the two databases genuinely differ - SQL dialect, strictness, replication, and how to actually choose between them.

MySQL/MariaDB in the cloud vs self-hosted

Managed MySQL and MariaDB providers, PlanetScale's serverless branching model, and applying the Module 6 decision framework here specifically.

MySQL & MariaDB Quiz

7 questions

Why NoSQL exists - the limits of the relational model

CAP theorem, horizontal scaling, and the real problems that pushed some systems away from strict relational tables.

The four types of NoSQL databases

Document, key-value, column-family and graph databases explained one at a time - what each is actually good at, with real examples.

MongoDB hands-on: your first document database

Installing MongoDB, the document model in practice, queries and aggregation compared directly against SQL you already know.

Redis hands-on: caching and beyond

Installing Redis, its core data structures, and the caching pattern behind almost every fast, high-traffic application.

Choosing the right database: a complete decision framework

A capstone lesson bringing together every database in this course into one practical framework, plus a worked real-world example.

NoSQL & Choosing the Right Database Quiz

8 questions

Views and materialized views

Saving a query as a reusable virtual table, the difference between a view and a materialized view, and when to reach for each.

Stored procedures, functions, and triggers

Moving logic into the database itself - reusable procedures, custom functions, and code that runs automatically on data changes.

Upserts, sequences, and generated keys

Inserting-or-updating atomically with ON CONFLICT, the race condition it prevents, and choosing between auto-increment IDs and UUIDs.

Recursive CTEs and hierarchical data, properly

A full, worked recursive CTE - org charts, category trees, and the base case/recursive case pattern explained step by step.

Classic SQL patterns: nth highest, duplicates, and gaps

The exact query patterns asked in real SQL interviews and needed in real reporting work - solved using everything from this entire course.

Advanced SQL Toolkit Quiz

9 questions

SQL syntax cheat sheet

Every core SQL statement, clause and pattern from this course in one place - DDL, DML, joins, aggregation, window functions and more - for quick reference.

PostgreSQL cheat sheet

psql meta-commands, roles and privileges, JSONB, arrays, full-text search, and connection strings - the PostgreSQL-specific reference for this course.

MySQL & MariaDB cheat sheet

The mysql command-line client, storage engines, users and hosts, and the exact syntax differences from PostgreSQL - a quick reference.

NoSQL cheat sheet: MongoDB and Redis

MongoDB CRUD and the aggregation pipeline mapped directly to SQL, plus Redis's core data structures and the cache-aside pattern - a quick reference.

Cheat Sheets Quiz

5 questions

Database Foundations Quiz

Database Foundations · 8 questions

SQL Fundamentals Quiz

SQL Fundamentals · 10 questions

Joins & Aggregation Quiz

Joins & Aggregation · 11 questions

Design & Normalization Quiz

Design & Normalization · 9 questions

Transactions & Performance Quiz

Transactions & Performance · 8 questions

PostgreSQL Deep Dive Quiz

PostgreSQL Deep Dive · 7 questions

MySQL & MariaDB Quiz

MySQL & MariaDB · 7 questions

NoSQL & Choosing the Right Database Quiz

NoSQL & Choosing the Right Database · 8 questions

Advanced SQL Toolkit Quiz

Advanced SQL Toolkit · 9 questions

Cheat Sheets Quiz

Cheat Sheets · 5 questions

SQL & Databases Final Assessment

Final assessment · 25 questions