Question

Peter Chen developed ERDs in 1976. Since then Charles Bachman and James Martin have added some slight refinements to the basic ERD principles. You should use the Crow’s foot notation for your diagrams. Describe the use of keys in the database. Can you have more than one key? Explain your answer.

Answer 1

Answer:

Check the explanation

Explanation:

In RDBMS relational database, the keys play an essential role in making the database reliable and relational in which two or more relations (tables) can be divided into a range of relations with the use of diverse types of keys due to which the redundancy decreases and flexibility of data storage increases.

The following are the usage of keys in a database:

   It helps in identifying a specific record that is present in the table.

   It is used in minimizing the redundancy from the tables.

   It is used in removing the multi-valued attributes from the relations.

   it helps in connecting one table with others by using Foreign keys.

   It is used in maintaining the uniqueness of the data stored in the database.

   It helps in identifying the relationship between two or more tables.

Types of keys in a relational database:

   PRIMARY KEY: It helps in identifying each record uniquely due to which the redundancy of data can be minimized.

   FOREIGN KEY: It is a kind of referenced key that helps in making a relationship between two or more tables. It helps in fetching records by combining two or more tables with the help of different joins.

   SUPER KEY: It is a combination of two or more keys that can be selected as primary. It may contain those columns which have repeated values.

   COMPOUND KEY: It is a combination of those columns which may not be used independently as the identification of unique records but their combination does.

   CANDIDATE KEY: It is a kind of a super key that does not contain repeated records. A primary key can be chosen from candidate keys.