Group by GROUPING SETS for custom rollups in Oracle

When you use GROUP BY with the summary functions like COUNT and SUM, you normally don't get multi-level totals. Each unique combination of the columns in the GROUP BY generates a total, but these totals aren't "rolled up" into higher level totals.

The article continues at http://builder.com.com/5100-6388_14-6134424.html?tag=sc