In SQL, window functions are a powerful tool for producing calculations that are dependent on data in other rows.

They allow you to attach data to the record without having to perform complex aggregations and joins.

In general, window functions are performed across a partition of records and return some computation about the record relative to the partition overall.

Currently, Arroyo supports the ROW_NUMBER() window function, and requires the partition include a time window so that there is a guarantee of completeness.

For example, to calculate the most common auction in a dataset over the last 10 minutes every second, you could use the following query:

        PARTITION BY window
        ORDER BY count DESC) as row_number, auction, count 
    FROM (
      SELECT auction,
             hop(INTERVAL '1' second, INTERVAL '10' minute ) as window,
             count(*) as count
        FROM bids
        GROUP BY 1, 2)) where row_number = 1