This page is a quick reference checkpoint for SUM OVER in BigQuery: behavior, syntax rules, edge cases, and a minimal example; plus the official vendor documentation.
SUM OVER returns the running or partitioned sum within the window frame.
When an aggregate function is used with the OVER clause it becomes a window function. If ORDER BY is present but no frame clause is given, the frame defaults to RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW.
If this behavior feels unintuitive, the tutorial below explains the underlying pattern step-by-step.
SUM([ DISTINCT ] expression) [ OVER over_clause ]
SELECT region, amount, SUM(amount) OVER (PARTITION BY region) AS region_sum FROM sales_table;
If you came here to confirm syntax, you’re done. If you came here to get better at window functions, choose your next step.
SUM 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 BigQuery Documentation →Looking for more functions across all SQL dialects? Visit the full SQL Dialects & Window Functions Documentation.