Determinants and Their Role in a Database

Determinants identify values assigned to other attributes

A determinant in a database table is an attribute that determines the values assigned to other attributes in the same row. By this definition, any primary key or candidate key is a determinant. However, there may be determinants that aren't primary or candidate keys.

An Example of a Determinant

For example, a company might use a table with the attributes Employee_id, First_name, Last_name, and Date of Birth.

Employee_id First_name Last_name Date of Birth

123

Megan Brown 01/29/1979
234 Ben Wilder 02/14/1985
345 Megan Chowdery 2/14/1985
456 Charles Brown 07/19/1984

In this case, the Employee_id field determines the remaining three fields. The name fields do not determine the primary key because the company might have employees who share the same first or last name. Similarly, the Date of Birth field does not determine the Employee_id or the name fields because employees may share the same birthday.

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Determinant Relationships to Database Keys

In this example, Employee_id is a determinant, a candidate key, and also a primary key. It's a candidate key because when searching the entire database for 234, the row containing Ben Wilder's information appears, and no other record is shown.

Another candidate key occurs when searching the database by the information in three columns: First_name, Last_name, and Date of Birth, which also retrieves the same result. 

Employee_id is the primary key because of all the combinations of columns that can be used as a candidate key, it is the easiest column to use as the primary reference to this table. Also, it is guaranteed to be unique to this table, no matter how many other employees there are, as opposed to the information in other columns. 

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