Candidate keys, Database Management System

Super keys of a relation can have extra attributes. Candidate keys are minimal super key, i.e. such a key have no extraneous attribute. An attribute is known as extraneous if even after removing it from the key, create the remaining attributes still has the properties of a key.

The following properties must be satisfied by the candidate keys:

  • A candidate key's value must exist. It cannot be null. (This is also known as entity integrity rule)
  • A candidate key has to be unique.
  • A candidate key is a smallest set of attributes.
  • The value of a candidate key has to be stable. Its value cannot change outside the control of the system.

A relation can have more than single candidate keys and one of them can be chosen as a primary key.

For instance, in the relation PERSON the two likely candidate keys are PERSON- ID and NAME (assuming unique names in the table). PERSON-ID may be taken as the primary key.

Posted Date: 3/6/2013 5:24:18 AM | Location : United States

Related Discussions:- Candidate keys, Assignment Help, Ask Question on Candidate keys, Get Answer, Expert's Help, Candidate keys Discussions

Write discussion on Candidate keys
Your posts are moderated
Related Questions
Example- Search the salary of employees who are not 'ANALYST' but get a salary below than or equal to any people employed as 'ANALYST'. SELECT EMPNO, ENAME, JOB, SAL FROMEMP

3NF Normal Form A relation schema R is in 3NF if it is in 2NF and for each FD X A either of the following is true X is a Super-key of R. A is a prime attribute of R

differences between a classified catalog and a dictionary catalog

What are the various forms of data transparency? a) fragmentation transparency b) replication transparency c) location transparency

how to make an e r diagram?

Explain the ACID properties of a transaction Ans: ACID properties are a significant concept for databases. The ACID stands for Atomicity, Consistency, Isolation, and Durability

While sorting, if the main storage available is not enough, the system writes data to an external help file.  The SAP profile parameter, which determines DIR_SORTTMP

Explain in detail about Collaboration Diagrams Collaboration diagrams are interaction diagrams which emphasize structural organisation of an object that transmit and receive m

Question: a) What is Client/Server and what benefits can be expected from Client/Server systems? b) Explain what middleware is and what it does. Why would MIS managers be p