A fact table is the central table in a star schema data warehouse. It contains foreign keys that join to dimension tables and measures containing analyzed data. Measures can be additive, semi-additive, or non-additive depending on whether they can be summed across all dimensions. A factless fact table is also possible, containing only dimension keys to represent intersections but no measures.

1. Fact Table Fact Types
&
Fact less Fact Table
Dr. R.Balamurugan

2. FACT TABLE
 A Fact Table is the central table in a star
schema of a data warehouse.
 It consists of two types of columns.
 The foreign keys column allows to join with
dimension tables .
 The measure columns contain the data that
is being analyzed.

3. FACT TABLE COLUMNS – FOREIGN KEY
 Foreign Key – Column Type
 These are the columns as coming from
Dimension Tables
 Are the primary keys of Dimension Tables

4. MEASURES OR FACTS
 Fact tables - Measures
 Collection of measurements on a specific
aspects of business
 sales amount, order quantity, profit, balance and
discount amount.

5. ADDITIVITY OF MEASURES
 A fact table might contain either detail level
facts or facts that have been aggregated.
 The primary purpose of Data warehouse is
reporting, and forecasting
 Many times reports are aggregations such as
sum
 Example: sales by quarter, by region,
 Many reports are usually aggregations

6. TYPES OF ADDITIVITY OF MEASURES
 Types of Additivity of Measures
 Additive measures
 Semi-additive measures
 Non-additive measures

7. ADDITIVE MEASURES
 Additive
 If a measure can be summed across all
dimensions
 The purpose of this table is to record the
sales amount for each product in each
store on a daily basis.
Date
Store
Product
Sales_Amount

8. SEMI-ADDITIVE MEASURES
Semi-additive
 Sometimes, we can sum a
measure across all
dimensions except for time
 such as account balance
 We can’t sum the account
balance across the time
dimension
Date
Account
Current_Balance

9. NON-ADDITIVE MEASURES
 Some measures
can’t ever be
summed
 These are called
non-additive
measures
 Such as discount
percentages and
prices
Date
Account
Profit_margin
 Profit_Margin is a
non-additive fact, for
it does not make
sense to add them
up for the account
level or the day level.

10. FACTLESS FACT TABLE
 In the real world, it is possible to have a fact
table that contains no measures or facts.
These tables are called "Factless Fact
tables".
 A factless fact table is a fact table that does
have only dimensions (keys).
 It is essentially an intersection of dimensions.

11. EXAMPLE
 The fact table would
consist of 3 dimensions:
the student dimension,
the time dimension, and
the class dimension.