# Set Operation

An operation combining compatible query results according to set rules.

## What is **Set Operation** in a relational database?

**Set Operation** — An operation combining compatible query results according to set rules.

```sql
SELECT email FROM customer
UNION
SELECT email FROM supplier;
```

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

Updated: September 27, 2026

Source: https://www.ask-codey.com/glossary/set-operation