Determinants and their role in the database

Determinants determine the values ​​assigned to other attributes

A qualifier in a database table is an attribute that can be used to determine the values ​​assigned to other attributes in the same row. By this definition, any primary or candidate key is a determinant, but there may be determinants that are not primary or candidate keys.

For example, a company can use a table of attributes, and .

emPLOYEE_ID
Name
Last name
Date of birth
TR>

123

td>

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


In this case, the field defines the remaining three fields. First name fields are not specified because the company may have employees with the same first or last name. Likewise, the field does not define fields or titles because employees can share the same birthday.

Deterministic relationships with database keys

In this example, these are the determinant, the candidate key, and also the primary key. This is a candidate key because searching the entire database for 234 returns a row of information about Ben Wilder and no other entries are shown. Another candidate key comes up when searching the database for information in three columns; and, which also gets the same result.

It is a primary key because of all combinations of columns that can be used as a candidate key, it is the easiest column to use as a primary reference to this table. It is also guaranteed to be unique to this table, regardless of the number of other employees, unlike the information in the other columns.

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