# Understanding Trivial Functional Dependency JGI/Jamie Grill/Getty Images

In the world of relational database theory, a functional dependency exists when one attribute determines another attribute uniquely in a database. A trivial functional dependency is a database dependency that occurs when describing a functional dependency of an attribute or of a collection of attributes that includes the original attribute.

### Examples of Trivial Functional Dependencies

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.

• {A,B} –> B is a trivial functional dependency because B is a subset of A,B. Since {A,B} –> B includes B, the value of B can be determined. It's a trivial functional dependency because determining B is satisfied by its relationship to A,B. 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 or Employee_ID –> Employee_ID,  and Employee_Name –> Employee_Name. These are all trivial functional dependencies.
• If a functional dependency X–>Y, and Y is a subset of X, this is a trivial functional dependency. If Y is not a subset of X, this is not a trivial functional dependency.