The relational model is one idea, but it's implemented by several real, independently-built products — each with its own history, licensing, and strengths. This chapter is a map of the ones you're most likely to actually encounter, before the next few chapters profile six of them specifically.
Why This Matters
Nothing in this course depends on which specific RDBMS product you eventually use — the relational model, SQL, and almost everything you'll learn are shared across all of them. Knowing roughly what each major product is known for is what lets you follow real-world conversations and job listings without getting lost in brand names that all describe fundamentally the same kind of database.
Core Concept
All of the products in this section are RDBMS — they all implement the relational model from the previous chapters. They differ in who built them, how they're licensed, which extra features they add on top of the standard, and which kinds of workloads they're historically best known for. None of these differences change anything you'll learn in the rest of this course about the relational model itself.
Deep Dive
- Some of these products are fully open-source (PostgreSQL, MariaDB, SQLite), some are open-source with a commercially-licensed enterprise version (MySQL), and some are fully commercial, proprietary products (Oracle Database, Microsoft SQL Server). This affects cost and support, not how the relational model works underneath.
- A few of these are full client-server databases meant to run on a dedicated server and serve many applications at once (PostgreSQL, MySQL, MariaDB, Oracle, SQL Server). One — SQLite — is fundamentally different: it's a lightweight, embedded database that runs inside your application itself, with no separate server at all, which is exactly why it's used for the SQL Playground elsewhere in this course.
Example
SIX RDBMS PRODUCTS, AT A GLANCE
| Product | License | Best Known For |
|---|---|---|
| MySQL | Open-source (with a commercial edition) | Web applications; historically paired with PHP |
| PostgreSQL | Open-source | Strict standards compliance and advanced features |
| MariaDB | Open-source | A community-driven fork of MySQL |
| Oracle Database | Commercial | Large enterprise systems |
| SQL Server | Commercial (with a free edition) | Microsoft-centric enterprise environments |
| SQLite | Open-source | Embedded, single-file databases with no server |
Production Perspective
In real job listings and codebases, you'll see teams choose between these products based on cost, licensing, existing team experience, cloud provider support, and specific feature needs — almost never based on "which one is more relational", because they all implement the same underlying model you're learning in this course.
Interview Questions
Are MySQL, PostgreSQL, and Oracle Database all RDBMS?
Yes — they all implement the relational model. They differ in licensing, extra features, and historical strengths, not in the fundamental way they organize data.
What makes SQLite fundamentally different from the other five products in this section?
SQLite is an embedded database that runs inside the application itself, with no separate server process — the other five are client-server databases designed to run on a dedicated server and serve many applications or users at once.
Chapter Summary
The relational model is implemented by several real products, each with different licensing and strengths, but the same underlying ideas. The next few chapters look at six of the most common ones you're likely to encounter.