Stage 2 of 7 · 11 lessons · ~3 months

Relational databases and SQL

Almost every backend is a careful wrapper around a relational database. Learn to model data, write SQL by hand, index it for real queries and understand what your ORM does on your behalf.

Start: Queries and joins

Lessons· one lesson for each topic, in this order

Start with· follow one of these

CoursePaid
Grokking Relational Database Design and Modeling
Design Gurus · Intermediate · $98 one-time
The modelling and normalisation decisions that stay with a codebase for years
CourseFree
CS50's Introduction to Databases with SQL
Harvard University · Beginner
Free course from querying through schema design, indexes, transactions and scaling

Practise

Grokking SQL for Tech InterviewsPaid
Structured SQL practice on joins, grouping and subqueries once the basics feel easy
PostgreSQL Exercises
Free SQL drills on one real schema, from simple selects up to recursive queries

Keep handy

SQLx Documentation
Query macros, pools, transactions, migrations and offline mode, with PostgreSQL examples

Also worth your time

Database Indexing Explained: B-Tree, Hash, Bitmap, R-Tree, and When to Use Each (opens in a new tab)Read
B-tree and composite indexes, plus the leftmost-prefix rule that trips people up
Grokking Database Fundamentals for Tech InterviewsGo deeperPaid
What sits under your queries: storage engines, transactions and isolation levels

Before moving on: Design a PostgreSQL schema for a small booking or ordering system, write the ten queries it needs by hand, add indexes and show with EXPLAIN ANALYZE that they are used.

Tauseef's advice

Write raw SQL first; with SQLx you may never need an ORM, and the query macros keep your SQL checked against the real schema. Learn on PostgreSQL; it is the safest default and what most new projects pick.