Empty OVER clauses

The OVER() clause does not require a windowing clause. If your query uses an analytic function like SUM(x) and you specify an empty OVER() clause, the analytic function is used as a reporting function, where the entire input is treated as a single partition; the aggregate returns the same aggregated value for each row of the result set. The query executes on a single node, potentially resulting in poor performance.

If you add a PARTITION BY clause to the OVER() clause, the query executes on multiple nodes, improving its performance.