Primary and foreign key, Database Management System

Assignment Help:

Primary Key

The primary key is the candidate key that is selected by the database designer as the principal denotes of identifying entities within an entity set. The left candidate keys, if any, are called as alternate keys.

Foreign Keys

Let us first tell you the basic definition of foreign key.

Let R2 be a relation, then a foreign key in R2 is a subset of the set of attributes of R2, such that:

1.   There be a relation R1 (R1 and R2 not essentially distinct) with a candidate key, and

2.   For all time, every value of a foreign key in the present state or instance of R2 is identical to the value of Candidate Key in a few tuple in the present state of R1.


Related Discussions:- Primary and foreign key

What are the disadvantages of relational data, What are the disadvantages o...

What are the disadvantages of relational data ? Disadvantages • Performance - If the number of tables among that relationships to be established are large and the tables t

Relationship cardinality, Cardinality shows the number of instances of an e...

Cardinality shows the number of instances of an entity associated with another entity participating in a relationship. Depend on the cardinality binary relationship can be further

Define database layer, Define Database layer? The database layer define...

Define Database layer? The database layer defines the data formats used in the database.

What is dml (data manipulation language)?, This language that enable user m...

This language that enable user manipulate to or access data as organized by appropriate data model. Low level or Procedural DML : DML needs a user to specify what data ar

What is trigger, What is Trigger? Trigger: A database trigger is proced...

What is Trigger? Trigger: A database trigger is procedural code which is automatically executed in response to specific events on a particular table in a database. Triggers can

Implementation of database, The ER diagram clearly showing the additional t...

The ER diagram clearly showing the additional tables you have implemented. SQL table creation scripts for the tables you have set up. SQL scripts showing the sample data you

Homework, can you resolve this for me please? Database Management Systems ...

can you resolve this for me please? Database Management Systems Homework 1 The following relations are given (primary keys are underlined): PLAY-ACTOR(AId, Name, Nationality, Birt

Define a relation schema, A Relation Schema represented by R(A1, A2, .....

A Relation Schema represented by R(A1, A2, ..., An) is made up of the relation name the list of attributes and R Ai that it contains. A relation is described as a set of tuples

Architectural standard, Architectural standard: Designation : Archit...

Architectural standard: Designation : Architect , Consultant Job Profile : As a part of Oracle Fusion Middleware at Satyam, I am involved with Presales, Delivery, A

Weak entity, An example of a weak entity is Staff because the availabilityI...

An example of a weak entity is Staff because the availabilityID cannot be uniquely identified unless it is used in conjunction with the foreign key known as availabilityID in the A

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