Databases
Schemas, queries, and the production lessons that come with them.
Watch it animated → Interactive, click-through walkthroughs for Databases concepts.Basic
What a Database Actually Is A database isn't a fancy spreadsheet - it's an organized store of data plus a program (the DBMS) that guards integrity, answers questions fast, and lets many people use it at once without stepping on each other.
SELECT, WHERE & Friends: Querying Basics How to read and change data with SQL: the SELECT query shape, filtering and sorting with WHERE/ORDER BY/LIMIT, and adding/changing/removing rows with INSERT/UPDATE/DELETE - without the career-defining accidents.
Relationships & Keys (Primary & Foreign) Why real data lives in several linked tables instead of one big one, what primary and foreign keys actually are, and how they let the database enforce that your records stay connected and consistent.
SQL Joins, Finally Explained What a JOIN actually is, why your data lives in separate tables in the first place, and how INNER, LEFT, and the others stitch those tables back together without surprising you.
Intermediate
Why Is My Query Slow? (Indexes & EXPLAIN) A query that's instant on your laptop crawls in production because the database is reading every row to find matches; an index lets it jump straight to them, and EXPLAIN lets you see which one is happening.
Transactions & ACID, Explained What a database transaction actually is, the four ACID guarantees in plain language, and what really goes wrong when transactions overlap - so you can make multiple changes all-or-nothing without losing sleep.
Database Migrations Without Fear What a migration actually is (git for your schema), the golden pattern for changing live data safely, and the dangerous migrations that lock tables or break the running app - so you can change a production schema without losing data or taking downtime.
SQL vs NoSQL, Plainly A fair, two-sided look at relational vs NoSQL databases - what each is actually shaped for, the real trade-offs, and how to choose without joining a holy war.
How an ORM Works Understand the pattern under every ORM - Hibernate, SQLAlchemy, GORM, EF Core - instead of memorizing one library's API: the object-relational mismatch, mapping objects to tables, the identity map and unit of work, change tracking and dirty checking, lazy loading and the N+1 trap, how a query builder becomes SQL, and when not to use an ORM at all. Language-agnostic, concept-first.
The N+1 Query Problem The ORM trap that is fast on seed data and dead in production: one query quietly becomes N+1. How to spot it and fix it.
Database Connection Pools Why too many connections takes down production, what a database connection actually costs, and how pool sizing keeps app and database alive.
Database Backups and Restores A backup you have never restored is a hope, not a backup. Logical versus physical dumps, point-in-time recovery, and testing the restore.
Advanced
Scaling a Database (Replication & Sharding) When one database box isn't enough: how to scale up and optimize first, scale reads with replication (and live with replication lag), and only then scale writes with sharding - and why sharding is the expensive last resort.