Window Functions #

A window function performs a calculation across a set of table rows that are somehow related to the current row.

This is comparable to the type of calculation that can be done with an aggregate function except it does not collapse the group of records into a single record.

Window functions create aggregates without flattening the data into a single row.

To define a window function:

select <aggregate_function> over (
  [ partition by <column_name> [ order by <column_name> ] ]
)

The partition by clause groups the records similar to the GROUP BY clause. The order by sorts the resulting window function records.