# One-to-One Relationship

A relationship where each row can relate to at most one row on the other side.

## What is **One-to-One Relationship** in a relational database?

**One-to-One Relationship** — A relationship where each row can relate to at most one row on the other side.

```sql
CREATE TABLE customer_profile (
    customer_id INTEGER PRIMARY KEY
        REFERENCES customer (customer_id)
);
```

Level: Novice · [More Database terms at this level](https://www.ask-codey.com/glossary/subjects/database/novice)

Updated: September 27, 2026

Source: https://www.ask-codey.com/glossary/one-to-one-relationship