Implementing Aggregartes for Dimensional DWH

Creating aggregate is usually summarizing and storing data which is available in the fact table in order to improve the performance of end user queries.

These are direct costs assocaited with this approach.the cost of storage on the system,the cost of processing to create the aggregates and the cost of monitoring aggregate usage,we are trading these costs aganist the need for query performance.

There are three approaches:

1.No aggregation.

2.Selective aggregation.

3.Exhaustive aggregation.

In some cases we need only small amount of data to get performance without aggregates.
but in typical database Datawarehouse,we need aggregate tables.

To  have aggregate tables to get query should get minimum number of records to return answer.