Trivial Functional Dependency

Trivial FD is a value that includes the original value

A trivial functional dependency is a database dependency that occurs when describing a functional dependency (FD) of an attribute or of a collection of attributes that includes the original attribute.

This kind of dependency is called trivial because it can be derived from common sense. If one "side" is a subset of the other, it's considered trivial. The left side is considered the determinant and the right the dependent.

See the examples below for more information.

Examples of Trivial Functional Dependencies

A --> B is a trivial FD only if B is a subset of A. Since "A --> B" includes B, as mentioned above, the value of B can be determined from A --> B. It's a trivial functional dependency because determining B is satisfied by its relationship to A, B. 

In other words, since the values of B are determined by the values of A, any other sequence that shares the values of A will have the exact same values as B. Another way to put it is that all of B is included in A, which is why it is A's subset. 

{Employee_ID, Employee_Name} --> Employee_ID is also a trivial functional dependency since Employee_ID is a subset of {Employee_ID, Employee_Name}.

The same is true for A --> A and C --> C, or Employee_ID --> Employee_ID and Employee_Name --> Employee_Name.

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Chapple, Mike. "Trivial Functional Dependency." ThoughtCo, Oct. 29, 2017, Chapple, Mike. (2017, October 29). Trivial Functional Dependency. Retrieved from Chapple, Mike. "Trivial Functional Dependency." ThoughtCo. (accessed January 23, 2018).