RELATIONAL DATA MODEL FUNDAMENTALS - Database Design and Development: An Essential Guide for IT Professionals - page 251

Note the symbol : used to perform the assignment of the result and name the

resulting relation as PATIENT-15. There are no keywords.

=

Union

Features and function

• Operates on two relations.
• Combines two relations.
• Both relations must be union-compatible; that is, they must have the same
columns.
• The result is a single relation containing rows and columns as indicated
below:
• Rows—all the rows from both relations, duly eliminating any duplicate rows
• Columns—same columns as in either of the original relations

Example

In the database of a medical center, there are two relations representing data
about the doctors. One relation, SUPVRDOCTOR, represents data about
doctors with supervisory responsibilities who have other doctors reporting to
them. The other relation SUBDOCTOR represents data about every doctor
who reports to another doctor. Figure 8-11 shows these two tables with data
in the rows and columns.

Data request List all the attributes of all the doctors in the medical center. Call
the result relation ALLDOCTOR.

DrID
10
14
23
37
39

DrName Specialty DrPhone

918-756-0831
609-238-3377
732-613-9313
609-246-0331
918-613-1988

SuprDrID
25
45
36
13
45

SUBDOCTOR
Relation

Kim Maggio Family Practice

Monika Isaac Neurology

Marcus Kulper Internal Medicine

Ira Goldman Psychiatry

Lawrence Stark Radiology

45 Robert Martin Surgery General 609-924-9248 25

36 Elaine Hsu Urology 908-535-5228 25

25 13 Leroy Richardson Oncology 908-322-5566

SUPVR DOCTOR
Relation

DrID
25
45
36

DrName Specialty DrPhone

609-238-5100
609-924-9248
908-535-5228

SuprDrID

Roger Smarts Neurology

Robert Martin Surgery General 25

25 Elaine Hsu Urology

13 Leroy Richardson Oncology 908-322-5566 25

Figure 8-11 SUBDOCTOR and SUPVRDOCTOR relations.