# One-to-One

How a one-to-one relationship uses the child table's primary key as its foreign key, and why you would move rarely used data into its own table.

![Cheat sheet: One-to-One](https://fsdtrainingmedia.blob.core.windows.net/public/images/2026/11/0f5ad3376c2040d0a5d8f3fc1ba2e058.webp)

- Category: SQL
- Level: Apprentice
- Tags: database, One-to-One Relationship, sql
- Updated: November 3, 2026

Source: https://www.ask-codey.com/cheat-sheets/database-relationships-one-to-one-cheat-sheet