RELATIONAL DATA MODEL FUNDAMENTALS - Database Design and Development: An Essential Guide for IT Professionals - page 256

PATIENT Relation BILLING Relation

BilledCharges
150.00
225.00
315.00
195.00

BldPatientNo
1234
2345
1234
2345

PatientNo
1234
2345
3456

DischargeDate
10-Feb
22-Feb
5-Mar

DISCHRGPATIENT Relation --- three types

PatientNo
1234
2345
1234
2345

DischargeDate
10-Feb
22-Feb
10-Feb
22-Feb

BldPatientNo
1234
2345
1234
2345

BilledCharges
150.00
225.00
315.00
195.00

Result of
equijoin

PatientNo
1234
2345
1234
2345

DischargeDate
10-Feb
22-Feb
10-Feb
22-Feb

BilledCharges
150.00
225.00
315.00
195.00

Result of
natural join

PatientNo
1234
2345
1234
2345
3456

DischargeDate
10-Feb
22-Feb
10-Feb
22-Feb
5-Mar

BilledCharges
150.00
225.00
315.00
195.00

Result of
outer join

Figure 8-15 JOIN operation.

connect these pieces of data across the two relations based on equal values in
PatientNo columns that are common to both relations. Natural join operation
accomplishes this task.
Also note the other two types of join operations illustrated in Figure 8-15.

Divide

Features and function

• Operates on two relations.
• The divide operation is the reverse of the product operation.
• The result is a single relation containing rows and columns as indicated
below:
• Rows—rows in one relation matching with every row in another relation
• Columns—all and only columns of the first relation,

but not of the

second

Example

Refer to Figure 8-16 for the discussion of this operation. Note the three relations
A, B, and C.
Divide relation B by relation C, giving A as the result relation. The following con-
ditions apply: