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Populating Star Schemas with Distributed SQL

Oracle Tips by Burleson Consulting

The Data Warehouse Development Life Cycle

Oracle Data Warehouse Design

POPULATING STAR SCHEMAS WITH DISTRIBUTED SQL

This is a very simple method for achieving the extraction, normalization, and insertion of the operational data into the STAR schema. Note that we can even handle computed values such as total_cost, which is price times quantity_sold. By specifying the SYSDATE in the WHERE clause, we ensure that only the day’s transactions are extracted and loaded into the STAR schema fact_table. Of course, we are still undertaking a very large five-way table join, but we would hope to run this extraction during off hours when the retrieval would not impact the production users.

But, what about rows that have been deleted? While uncommon, we still need to account for the possibility that some orders may be canceled. We need a mechanism for updating the STAR schema to reflect these deletions. The most obvious method for removing deleted orders from the STAR schema is to utilize Oracle triggers to create a DELETE trigger on the ORDER table of the operational system. This DELETE trigger will fire off a remote delete from the trigger to delete all rows from the STAR schema that are no longer valid, as follows:

CREATE TRIGGER delete_orders
AFTER DELETE ON ORDER
AS
(DELETE FROM fact_table@london
SEE CODE DEPOT FOR FULL SCRIPT
);

We now have a mechanism for keeping our data warehouse in relative synchronization with the operational database.


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
 

 


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