Page 40 - DCAP402_DCAO204_DATABASE MANAGEMENT SYSTEM_MANAGING DATABASE

Unit 2: Database Relational Model

SELECT *.D * .P Notes
1 1
FROM Department D , FULLOUTER JOIN Project P
1 1
WHERE D .PNo = P .PNo
1 1
The following table shows the result

Dept_Mid DNo PNo (PNo) Pname

101 2 11 11 A
97 5 22 22 B
120 4 33 NULL NULL
NULL NULL NULL 44 D

In this relation as you can see all the matched and unmatched columns of both the tables are
displayed, the values for the unmatched attributes are entered as NULL.

Division

To understand the concept of division operator consider a simple example of two relations with
attributes customer name, product id.
1. Customer (Customer name, product id)
2. Product (Product id)

The result of applying the division operator on relations customer and product is shown in the
“Result” relation.
A division operator returns a relation (result). That is a collection of rows from first relation
(customer) such that for every value in second relation (product). There exists a pair (customer
name, product id) in the first relation (customer).
Customer/product = Result
(Customer, Product)
= Custmername
(Product id)

Customer Product Result = customer/product
Customer name Product id Product id Customer name
Ravi 1021321 1021321 Ravi

Kumar 30991231 30991231 Sharma
Girish 2310219 Kumar
Sharma 1021321 Rahul
Rahul 30991231

The division operation is reverse of cartesian product. We can note that
(Customer/product id) = (customer name) * (product id)

Customer = Result * Product
A binary relationship sets is a relationship between only two entities.

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