Ricky L. answered • 04/01/20
Active Enterprise Financial Technology Consultant with SQL Experience
Unary relationships are fundamentally just relationships of the same entity to itself. In other words, relationships inside of one data table. A very useful example would be the relationship between different levels of employees in a company.
From the company's point of view, everyone is an employee. As a result, it makes almost no sense to make a bunch of different entity types / data tables for different levels of management.
Check out this quickie table below:
Employee_ID Name Manager_ID
1 Bob (Null)
2 Jane 1
3 Tim 1
4 Sarah 2
5 Rich 3
As you can see, Bob must be the CEO or a top level manager since he is not managed by anyone. On the other hand, Jane and Tim are likely mid level managers since they directly report to Bob. Further, Sarah and Rich may be team leaders who report up to their respective mid-level manager.
This example illustrates the idea of a unary relationship where employees relate to one another. I know it is very simplified but I hope that it helps :)
