A Fact Table in a dimensional model consists of one or more numeric facts
of importance to a business. Examples of facts are as follows:
- the number of products sold
- the value of products sold
- the number of products produced
- the number of service calls received
Businesses have a need to monitor these "facts" closely and to sum them
using different "dimensions". For example, a business might find the
following information useful:
- the value of products sold this quarter versus last quarter
- the value of products sold by store
- the value of products sold by channel (e.g. phone, Internet,
in-store shopping)
- the value of products sold by product (e.g. blue widgets, red
widgets)
Businesses will often need to sum facts by multiple dimensions:
- the value of products sold store, by product type and by day of week
- the value of products sold by product and by channel
In addition to numeric facts, fact table contain the "keys" of each of
the dimensions that related to that fact (e.g Customer Nbr, Product ID,
Store Nbr). Details about the dimensions (e.g customer name, customer
address) are stored in the dimension table (i.e. customer)
