Oracle Tips  by Burleson Consulting

The Data Warehouse Development Life Cycle

Aggregating Data For The Oracle Warehouse
Using SQL To Create Summary Tables

If we keep our summary tables in the same database as our data warehouse, it becomes easy to create the summary tables. In the following example, you can see how we can easily use Oracle SQL to create our tables:

CREATE TABLE month_by_customer_name
AS
SELECT month, customer_name, sum(total_sales)
FROM fact
GROUP BY customer_name;

CREATE TABLE region_by_item
AS
SELECT region, item_number, sum(total_sales)
FROM fact
GROUP BY item_number;

Note: These summary calculations may invoke full-table scans against your data warehouse and may also use a very large sort area, requiring sorting to disk. Because of the intense nature of these queries, you will want to ensure that these summary tables are created during off hours. For more information about tuning the creation of summary tables, see Chapter 12, Tuning Oracle SQL.

Now that you see how easy it is to create summary tables, note that it would be very easy to parameterize the Oracle SQL to allow the dimension names to be replaced by symbolic variables. For example:

CREATE TABLE &1_by_&2
AS
SELECT &1, &2, SUM(total_sales)
GROUP BY &2;

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This is an excerpt from "High Performance Data Warehousing". To learn more about Oracle, try "Oracle Tuning: The Definitive Reference", by Donald K. Burleson.  You can buy it direct from the publisher at 30% off here:
http://www.rampant-books.com/book_1002_oracle_tuning_definitive_reference_2nd_ed.htm