# UNION

A set operation combining compatible query results and removing duplicate rows.

## What is **UNION** in a relational database?

**UNION** — A set operation combining compatible query results and removing duplicate rows.

```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/union