On Tue, 2002-08-13 at 09:25, Bruce Momjian wrote:
>
> There is a web page about "star joins" used a lot in data warehousing,
> where you don't know what queries are going to be required and what
> indexes to create:
>
> http://www.dbdomain.com/a100397.htm
>
> They show some sample queries, which is good. Here is some
> interesting text:
>
> Star Transformation
>
> If there are bitmap indexes on SALES_REP_ID, PRODUCT_ID, and
> DEPARTMENT_ID in the SALES table, then Oracle can resolve the query
> using merges of the bitmap indexes.
>
> Because Oracle can efficiently merge multiple bitmap indexes, you can
> create a single bitmap index on each of the foreign-key columns in the
> fact table rather than on every possible combination of columns.
Another way to achive the similar result would be using segmented hash
indexes, where each column maps directly to some part of hash value.
> This
> lets you support all possible combinations of dimensions without
> creating an unreasonable number of indexes.
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Hannu