Set difference, Database Management System

Set Difference

If R1 and R2 are two union compatible relations or relations then result of R3 =R1- R2 is the relation that have only those tuples that are in R1 but not in R2.

Incase, R3 will have tuples such that R3 = {t | R1 ∋ t ∧ t∉R2}.

 

Example:

 

R1

 

X

Y

A1

B1

A7

B7

A2

B2

A4

B4

 

 

 

  R2  

A

B

A1

B1

A2

B2

A3

B3

A4

B4

 

 

R1-R2 =

 

 

 

R1-R2 =

A

B

A3

B3

 

R2-R1=

 

 

 

R2-R1=

A

B

A7

B7

 

 

 

Note: -1) Difference operation is not commutative, i.e.,

 R1 - R2 ≠ R2 - R1

2) Difference operation is not associative, i. e.,

R1 - (R2 - R3) ≠ (R1 - R2) - R3

Posted Date: 3/6/2013 5:46:06 AM | Location : United States







Related Discussions:- Set difference, Assignment Help, Ask Question on Set difference, Get Answer, Expert's Help, Set difference Discussions

Write discussion on Set difference
Your posts are moderated
Related Questions
properties of derirable decomposition

Explain the integrity constraints: Not Null,  Unique, Primary Key with an example each. Is the combination 'Not Null, Primary Key' a valid combination. Justify. Not Null - Shou

The Maximum no of key fields that can be used in a header is?? 50

Most computer systems authenticate users by asking them for the user name and password. However, the user names and passwords often can be guessed by hackers. Suggest an automated,


Availability: A site having the copy of a replicated relation fails, even then the relation may be found in another site. Therefore, the system may carry on to process at least th

let us consider a table having 2200 records and the fixed size of the table to be considered as 25.then how many numbers of table is requredto perform horizontal fragmentation

Define Query Processing Query processing is the process of selecting the best plan or strategy to be employed in responding to a database request. The plan is then executed to

Example RELATION SCHEMA for STUDENT: STUDENT (Roll No: string, name: string, login: string, age: integer) RELATION INSTANCE

What is multiplicity in the associations? Give an example to explain multiplicity? Multiplicity in association indicate number of objects participate in any relationship. For