# Database Relationships: an overview

The three kinds of relationship between tables (one-to-many, one-to-one and many-to-many) and how a diagram shows each.

Apprentice · SQL · Database · Updated October 29, 2026

Tables are linked to each other through relationships. There are three different types of theoretical relationships in a database.

![One-to-many in crow's foot notation: a single bar at the parent end, a crow's foot at the child end](https://fsdtrainingmedia.blob.core.windows.net/public/images/2026/09/ecc6647c8af94d829c0b8387d25556f0.png)

- **One-to-Many:** a row in a parent table can be related to many rows in a related child table

![One-to-one in crow's foot notation: a single bar at both ends](https://fsdtrainingmedia.blob.core.windows.net/public/images/2026/09/240ac4b54b824d2daed7fac53bfb7fa8.png)

- **One-to-One:** a row in a parent table can be related to only one row in a related child table

![Many-to-many in crow's foot notation: a crow's foot at both ends](https://fsdtrainingmedia.blob.core.windows.net/public/images/2026/09/1f23dfb401f74479bb2be88ae988ad2a.png)

- **Many-to-Many:** multiple rows in one table can be related to multiple rows in another. In this scenario, both tables act as both parent and child.

## Key terms

- [Relationship](https://www.ask-codey.com/glossary/relationship)
- [One-to-Many Relationship](https://www.ask-codey.com/glossary/one-to-many-relationship)
- [One-to-One Relationship](https://www.ask-codey.com/glossary/one-to-one-relationship)
- [Many-to-Many Relationship](https://www.ask-codey.com/glossary/many-to-many-relationship)

Source: https://www.ask-codey.com/lessons/database-relationships-an-overview