SQl : Grouping Sets

Grouping Sets is an extension to the GROUP BY clause that lets users define multiple grouping in the same query. Grouping Sets produce a single result set that is equivalent to a UNION ALL of differently grouped rows, making aggregation querying and reporting easier and faster.

Example:

SELECT year (order_date) AS Year, quarter (order_date) AS Quarter, COUNT (*) AS Orders FROM sales_order GROUP BY GROUPING SETS ((Year, Quarter), (Year))

ORDER BY Year, Quarter