---
source: https://iinventedlight.com/library/notes/postgres-window-functions.md
title: "PostgreSQL window functions: OVER, PARTITION BY, ORDER BY"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "PostgreSQL License; restated in our own words"
attribution: "Summary by iinventedlight (AI-assisted). Sources: PostgreSQL Global Development Group, PostgreSQL docs 3.5: Window Functions, PostgreSQL License; PostgreSQL Global Development Group, Window Functions, PostgreSQL License."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-04
status: published
checked_on: 2026-11-05
as_of: 2026-11-05
confidence: medium
untested: "Steps and code were not run; only the fetched documentation page was read."
category: coding-references
topic_area: "code-backend: SQL window functions"
tags: sql, postgresql, window-functions, database
sources:
  - id: S1
    title: "PostgreSQL docs 3.5: Window Functions"
    publisher: PostgreSQL Global Development Group
    url: https://www.postgresql.org/docs/current/tutorial-window.html
    accessed: 2026-11-05
    license: "PostgreSQL License"
  - id: S2
    title: "Window Functions"
    publisher: PostgreSQL Global Development Group
    url: https://www.postgresql.org/docs/current/functions-window.html
    accessed: 2026-11-05
    license: "PostgreSQL License"
    license: "PostgreSQL License"
---
# PostgreSQL window functions

## Short answer
A window function computes across related rows while still returning one result per input row. You always write an `OVER` clause. [S1][S2]

## Sketch
```sql
SELECT dept, name, salary,
       rank() OVER (PARTITION BY dept ORDER BY salary DESC)
FROM employees;
```

## Points
- Unlike grouped aggregates, window functions do not collapse rows. [S1]
- Without `PARTITION BY`, the window is the whole result set. [S1]
- Built-in window functions need window syntax (`OVER`). [S2]
- Ordinary aggregates can also be used as window functions with `OVER`. [S2]

## Claims
- id: C1
  claim: A window function calculates across a set of rows.
  source: S1
  evidence: "A window function performs a calculation across a set of table rows"
- id: C2
  claim: Window functions do not collapse rows into one output.
  source: S1
  evidence: "window functions do not cause rows to become grouped into a single output row"
- id: C3
  claim: Built-in window functions require an OVER clause.
  source: S2
  evidence: "an OVER clause is required"
- id: C4
  claim: Ordinary aggregates can act as window functions.
  source: S2
  evidence: "ordinary aggregate (i.e., not ordered-set or hypothetical-set aggregates) can be used as a window"

## Sources
- [S1] PostgreSQL docs 3.5: Window Functions. PostgreSQL Global Development Group. https://www.postgresql.org/docs/current/tutorial-window.html . License: PostgreSQL License. Accessed 2026-11-05.
- [S2] Window Functions. PostgreSQL Global Development Group. https://www.postgresql.org/docs/current/functions-window.html . License: PostgreSQL License. Accessed 2026-11-05.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

Source notice: PostgreSQL documentation, Portions Copyright (c) 1996-2026, The PostgreSQL Global Development Group; Portions Copyright (c) 1994, The Regents of the University of California. Used under the PostgreSQL License (https://www.postgresql.org/about/licence/).