Describe the composite key, Database Management System

Assignment Help:

Describe the Composite Key

Composite Key: Sometimes one key is not enough to uniquely recognize a row. E.g. in a single class Roll is enough to search a student, but in the whole school, merely searching by the Roll is not enough, because there could be 10 classes in the school and every one of them may have a certain roll no 5. To uniquely recognize the student we have to say something like "class VII, roll no 5". So, a combination of two or more attributes is combined to make a unique combination of values, such as Class + Roll.

 


Related Discussions:- Describe the composite key

Define and differentiate among ordered indexing and hashing, Define and dif...

Define and differentiate between ordered indexing and hashing. Ans: Ordered indexing: To gain fast random access to records in a file, we can make of an index structure. Every

Define the division operation of relational algebra, Define the Division Op...

Define the Division Operation of Relational Algebra Let R be a relation comprising attributes (A1,...Ap,Ap+1,...An) and S comprising attributes (Ap+1,...An)  DEF: Division

Describe specialsation and generalization, Describe Specialsation and gener...

Describe Specialsation and generalization? Specialisation /generalization: This is a top down and bottom up approach to the design of database. It displays the IS_A relation

Relational model, A model in database system mostly defines the organisatio...

A model in database system mostly defines the organisation of data or structure and a set of operations on that data. Relational model is a easy model in which database is represen

Give expression in both tuple calculus and domain calculus, Consider the fo...

Consider the following relational schema: Doctor(DName,Reg_no) Patient(Pname, Disease) Assigned_To (Pname,Dname) Give expression in both Tuple calculus and Domain calculus for

Er diatgrams, Ask q“A database will be made to store information about pati...

Ask q“A database will be made to store information about patients in a hospital. On arrival, each patient’s personal details (name, address, and telephone number) are recorded wher

Sorting field groups we cannot use more than one key field, While sorting f...

While sorting field groups we cannot use more than one key field False.

Describe the ways for selecting data structure, Ways for Selecting Data Str...

Ways for Selecting Data Structure Algorithms operate on data structure. Therefore, selection of the best algorithm means selecting the best data structure from whole bunch. Th

Relational algebra, Relational Algebra is a set of basic operations used to...

Relational Algebra is a set of basic operations used to influence the data in relational model. These operations allow the user to specify basic retrieval request. The result of re

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd