PostgreSQL Foundations·A database you can operate

The relational model and psql

PostgreSQL stores rows in tables and enforces relationships with keys.

Intermediate 13 min read Lesson 6 of 300 Challenge included

What you will be able to do

Use meaningful primary keys; UUIDs help when clients create records.
Add NOT NULL and CHECK constraints at the database boundary.
Use \d and \dt in psql to inspect objects.

In plain English

A primary key identifies a row; a foreign key points at another table. Constraints are executable documentation. psql gives you a direct, reproducible way to inspect schema and data.

schema.sqlSQL

create table courses (
  slug text primary key,
  title text not null,
  published boolean not null default false
);

create table lessons (
  id bigint generated always as identity primary key,
  course_slug text not null references courses(slug) on delete cascade,
  slug text not null,
  title text not null,
  minutes integer not null check (minutes > 0),
  unique (course_slug, slug)
);

Your turn

Create a lessons table

Medium

Create lessons with an identity id, a course_slug foreign key, a slug, a title and positive minutes. Make course_slug + slug unique.

SQL · starter

create table lessons ();

Check your understanding before moving on.

Knowledge checkQuestion 1

What does a foreign key enforce?

Select an answer to continue

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Next: Types, NULL and schema design

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