Functional Dependency in RDBMS

The normalization theory is based on  the fundamental notion of fundamental dependency. First, let’s examine the concept of functional dependency.

Given a relation R, attribute A is functionally dependent on attribute B if each value of A in R is associated with precisely one value of B.

In other words, attribute A is functionally dependent on B if and only if, for each value of  B, there is exactly one value of A..

Atrribute B is called the determinant.

Consider the following table EMPLOYEE.

Given a particular value of CODE, there is precisely one corresponding value for NAME. For example, for CODE E1, there is exactly one value of NAME, Mac. Hence, NAME is functionally dependent on CODE. Similarly. There is exactly  one value of CITY for each value of CODE. Hence, the attribute CITY is functionally dependent on the attribute CODE. The attribute CODE is the determinant. You can also say that CODE determines  CITY and NAME.