Defining relationships

Joining Data in SQL

Maham Faisal Khan

Senior Content Developer, DataCamp

One-to-many relationships

A diagram showing three books (Persuasion, Pride and Prejudice, and Emma) connected to one author, Jane Austen.

One-to-many relationships

One-to-one relationships

A diagram showing that one fingerprint can only be associated with one traveler.

One-to-one relationships

Many-to-many relationships

A diagram showing that many languages can be associated with many countries, and many countries can be associated with one language. Belgium has three official languages: French, German, and Dutch. Conversely, languages can be official in many countries: Dutch is an official language of both the Netherlands and Belgium, but not Germany.

Let's practice!

Joining Data in SQL