Add lesson 27: UUIDs and domains

[exekias]

Adds the fifth and final lesson of Module 6: Postgres power types — UUIDs and domains (roadmap item 27-uuid-and-domains).

What's in the lesson

• The uuid type and gen_random_uuid() (core, no extension) as a default primary key
• UUID vs bigint/serial tradeoffs (uniqueness / unguessability vs 16 bytes and random-insert index locality); UUIDv7 mentioned conceptually
• Enum types (CREATE TYPE … AS ENUM, ordering, ALTER TYPE … ADD VALUE)
• Domains: CREATE DOMAIN = a base type + a reusable CHECK (email, positive_int, and a NOT NULL domain) — write the rule once, enforce it everywhere

Seed

A couple of small tables using a uuid PK, an enum column, and domains.

Checks

One schema-state check: accounts.id is of type uuid.

Notes

Includes the byte-identical Module 6 module.yaml.

npm run lessons:validate and next build both pass.

Part of #6

🤖 Generated with Claude Code

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
learn-postgres	Ready	Preview	Jul 2, 2026 9:25am