Q: There is a reporting need for cost-price comparison in various currencies. The current exchange rates may not be available while loading currency-wise cost-price in the fact table. In such cases historical rates are used for calculation and a flag is set. Whenever current exchange rates become available (in a dimension table), all the records with flag set in the fact table should get updated physically (no history required). Query runtime calculation of cost-price is not preferable due to large amount of data. What should be done in such a scenario to avoid unnecessary data processing of fact table data?
When I've seen these types of problems, it sometimes makes sense to normalize theprocess and store the date along with the currency type in the fact able and then a dimension table with a simple lookup of date and currency value. With the appropriate indexes, this should be a very quick (single I/O) lookup during the query.It's important to implement the physical database design correctly to prevent full-table scans.
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