This page is a quick reference checkpoint for COUNT OVER in Postgres: behavior, syntax rules, edge cases, and a minimal example; plus the official vendor documentation.
COUNT OVER returns the number of rows in the window frame.
When a window aggregate is used with ORDER BY and the default frame, it produces a running-sum type behavior; to aggregate over the whole partition omit ORDER BY or specify ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING.
If this behavior feels unintuitive, the tutorial below explains the underlying pattern step-by-step.
Any ordinary aggregate (such as COUNT) can be used as a window function with an OVER clause.
SELECT COUNT() OVER (PARTITION BY department) FROM employees;
If you came here to confirm syntax, you’re done. If you came here to get better at window functions, choose your next step.
COUNT OVER is part of a bigger window-function pattern. If you want the “why”, start here: Aggregate Window Functions
Reading docs is useful. Writing the query correctly under pressure is the skill.
For the authoritative spec, use the vendor docs. This page is the fast “sanity check”.
View Postgres Documentation →Looking for more functions across all SQL dialects? Visit the full SQL Dialects & Window Functions Documentation.