# Aggregate Function

A function that summarizes a set of rows into one value.

## What is **Aggregate Function** in a relational database?

**Aggregate Function** — A function that summarizes a set of rows into one value.

```sql
SELECT customer_id, COUNT(*) AS order_count
FROM purchase_order
GROUP BY customer_id;
```

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/aggregate-function