Union - basic set operation, Database Management System

UNION

If R1 and R2 are two union compatible relations then R3 = R1 ∪ R2 is the relation having tuples that are either in R1 or in R2 or in both.

In case, R3 will have tuples such that R3 = {t | R1 ∋ t ∨ R2 ∋ t}.

Example

R1                                                                               

 

X

Y

A1

B1

A7

B7

A2

B2

A4

B4

R2

A

B

A1

B1

A2

B2

A3

B3

A4

B4

R3 = R1 ∪ R2 is

 Q

A

B

A1

B1

A2

B2

A3

B3

A4

B4

A7

B7

 

 

Note:  1) Union is a commutative operation, i.e, R ∪ S = S ∪ R.

2) Union is an associative operation, i.e.

R ∪ (S ∪ T) = (R ∪ S) ∪ T.

Posted Date: 3/6/2013 5:43:59 AM | Location : United States







Related Discussions:- Union - basic set operation, Assignment Help, Ask Question on Union - basic set operation, Get Answer, Expert's Help, Union - basic set operation Discussions

Write discussion on Union - basic set operation
Your posts are moderated
Related Questions
folding method and mid square method using visual basic

Describe the shadow paging technique.

Explain Authorization and Integrity Manager ? Authorization and Integrity Manager: Tests for the satisfaction of integrity constraints and checks the authority of users to acce

What is the main difference between read-only and update methods? A read-only method does not affect the values of a variable in an object, whereas an update method may alter t



Define- relational algebra. The relational algebra is a procedural query language. It having of a set of operations that take one or two relation as input and make a new relati

Advantages And Drawbacks Of Ddbms  There are various reasons for building distributed database systems, with sharing of data, reliability and availability, and speedup of query

The Update Operations : Update operations are used for altering database values. The constraint violations faced by this operation are logically the similar as the problem faced

Define Signal. It allows methods to respond to events triggered by themselves or by other processes. Each signal corresponds to an exacting event. A signal is represented in Sy