What is the Factless Fact table and purpose of Factless Fact Table?

Factless Fact table:

A) A Fact table without measures (numeric data) for a column is called Factless Fact table.

B) Fact table contains only id, keys and description columns and not measures are known as factless fact tables.

 

Purpose:

Generally factless fact table used when events that happen only at information level but not included in the calculations level. Just information about an event that happen over a period.

This type of fact table itself can be used to generate the useful reports such as count the number of occurrences with various criteria.  For example, factless fact table to capture the student attendance. The following questions can be answered:

Which class has the least attendance?

What is the average number of attendance of a given course?

All the queries are based on the COUNT () with the GROUP BY queries.  I think that the interesting metrics are the nested GROUP BY so you can first count and then apply other aggregate functions such as AVERAGE, MAX, MIN.