15.00 - Solving the Problem By Taking Simple Projections - Teradata Database

Teradata Database Design

prodname
Teradata Database
vrm_release
15.00
category
User Guide
featnum
B035-1094-015K

Solving the Problem By Taking Simple Projections

The particular problem with nulls in this table is readily resolved with a minor change in the logical design of the database. Because the attributes in this employee table are a combination of those that apply to all tuples and those that apply only to some tuples, the relationship is similar to that of a simple entity supertype and subtype, the difference being that the attribute in question, salary, is not unique: all employees receive a salary.

The following tables resolve the problem of multiple simultaneous semantics for the original employee table by taking projections from the original employee table:

 

employee

 

employee_salary

emp_num

emp_name

dept_num

hire_date

 

emp_num

salary

PK

 

 

 

 

PK

 

214

Smith

32

09-12-1989

 

214

56150

447

Lau

15

05-30-1993

 

103

29775

103

Hossein

09

09-13-1984

 

500

84932

500

Nakamura

11

06-09-1997

 

 

 

713

Schroeder

24

10-29-2001