definition

Fact table is the primary table in a dimensional model, it included one FK and measures. This Fk link with other dimensional tables.
Also, we can summarize those numeric measures and provide information about the history of the organization.

type

• addictive
  Additive facts are facts that can be summed up through all of the dimensions in the fact table
  eg: A sales fact is a good example for additive fact.

• Semi-Additive:
  Semi-additive facts are facts that can be summed up for some of the dimensions in the fact table, but not the others.

eg: balance amounts are common semi-additive facts because they are additive across all dimensions except time.

• Non-Additive:
  Non-additive facts are facts that cannot be summed up for any of the dimensions present in the fact table

eg: Facts which have percentages, ratios calculated.

• Factless Fact Table

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example

addictive
semi addictive
non addictive

• quantity, sales amount is additive, because it can be added by date, by store, by product
• quantity in hand is semi addictive, because it can be added by store, by product,
  but it can not be added by date, cause it denotes snap sorts of a level or balance at one point of time
• unit price & sales tax are non addictive

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