# Window Function

A function calculating across related rows without collapsing them into one row per group.

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

**Window Function** — A function calculating across related rows without collapsing them into one row per group.

```sql
SELECT order_id,
       SUM(total_amount) OVER (PARTITION BY customer_id) AS customer_total
FROM purchase_order;
```

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

Updated: September 27, 2026

Source: https://www.ask-codey.com/glossary/window-function