A Comprehensive Guide to DBMS Keys and Their Diverse Types

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Facebook generates 4 petabytes of data every day, which is like 167000 Gygabites every hour and all that data needs to be stored in a way that when required should be available within a few clicks. this complex task is made possible through different Keys in DBMS, for better understanding let’s dive deep into the concept of Keys in DBMS and Their Diverse Types.

A Database represents a large collection of records and Keys in DBMS are like special labels for identifying each row in a table. Databases are huge and there is always some possibility of duplication due to the large quantity of data, and different keys in DBMS resolve this issue by establishing relationships between different tables by providing a unique identifier. 

Keys in a DBMS are essential they keep data organized and make it easy to find data whenever required, apart from this different keys in DBMS are vital components of data integrity constraints on DBMS. now we have understood what are Keys in DBMS let’s dive deeper to explore various types of Keys in DBMS with suitable examples:

Diverse types of Keys in DBMS:

Primary Key

Primary keys in DBMS are like a special ID for each row in a table that identifies each record in the table. The primary key establishes the relationship between tables and makes it easy to relate between different attributes in two or more different tables.

For an attribute to qualify as a primary key:

1. It must not contain any duplicate values.
2. The value in any row not not be “null.” 

Let’s understand it with an example:

Student ID	Student name	Class 1
001	A	Science
002	B	Chemistry
003	C	Social science
004	A	English

In the above example, Student ID can be taken as the Primary key as it uniquely identifies values in each row and none of the values are null.

Super Key

Super keys in DBMS are the combination of one or more attributes in a table that uniquely identifies each record in a table. A super key is a Super Key that contains more information than required to uniquely identify each record in a table.

A Super Key is the superset of a primary key, and a Primary key is a minimal Super Key. For better understanding let’s understand it with an example:

Student ID	Student name	Class 1	Student e-mails
001	A	Science	[email protected]
002	B	Chemistry	[email protected]
003	C	Social science	[email protected]

In the above example, students can be identified by student ID as well as Student e-mails, they both act as a unique identifier so in this case the Super key = Student ID + Student e-mail.

Candidate Key

A candidate keys in DBMS are a column or a set of columns that can used to uniquely identify each record in the table. Candidate keys are just like Primary keys and have all the properties of a primary key, they must also qualify for two conditions required for the primary keys (unique identification of each record and no null values).

All candidate keys are super keys, but not all super keys are candidate keys, because super keys may sometimes contain data that is not necessary to uniquely identify each record in the column.

A table can contain multiple candidate keys but only one of them will chosen to be the primary key, Candidate Key provides an alternative choice of the primary keys; For better understanding let’s understand it with an example:

ISBN	Book Title	Author	Gener
001	A	Q	M
OO2	B	Q	N
003	C	R	O

In the above example, “ISBN” and the “Book Title” can uniquely identify each record and none of them contains null values, hence they both are Candidate keys.

Alternate Keys

Alternative keys in DBMS in the DBMS act as a backup key, that can also identify each record in the table uniquely apart from the primary key. There can be multiple alternate keys, unlike the primary key.

Candidate keys and alternate keys are very similar with a small difference, “Candidate keys are the primary key contender, whereas the Alternate keys are the backup option for uniquely identifying each record.”

All the Candidate keys are Alternate keys but not all Alternate keys are Candidate keys. For better understanding let’s understand it with an example:

Student ID	Student name	Class 1	Student e-mails
001	A	Science	[email protected]
002	B	Chemistry	[email protected]
003	C	Social science	[email protected]

In the above example, “Student ID” and “Student e-mails” can uniquely identify each record and both fulfill the condition of no null value, hence they both can be primary keys. In case the Student ID is chosen as the primary key, Student e-mails Become the Alternate key and Visa-versa.

Foreign Key

Foreign keys in DBMS are attributes that establish a relationship between two tables. Or in simpler words a bridge that connects the info in one column in a table to info from another column in another table.

A Foreign key helps maintain data accuracy by ensuring that the values entered in the foreign key column exist in the primary key column in the referenced table and prevent inconsistency in the database. For better understanding let’s understand it with an example:

Table 1: Table of Orders

Order ID	Customer ID	Order date	Value
001	A1	P	500/-
002	B1	Q	1200/-
003	C1	R	950/-

Table 2: Table of Customers 

Customer name	Customer ID	E-mail
M	A1	[email protected]
N	B1	[email protected]
O	C1	[email protected]

In the above example, Table 1 contains the information related to orders, and Table 2 contains the info about customers, if we have to extract the info about the e-mails of a particular order ID, we can easily do it by establishing a relationship as the column of Customer ID acts as a foreign key in table 2. 

By accurately representing table relationships it makes data quiring and data revival easy and efficient.

Composite key

This key in DBMS is the unique Combination of two or more columns that when taken together, can uniquely identify each record in a table are is a Composite key. Composite keys act as a tag that combines multiple attributes to create a unique identification for each record in a table.

Composite keys are helpful where a single key can not guarantee the unique identification of each record in the table; however, combining multiple attributes can create a unique identifier for each record. For better understanding let’s understand it with an example:

First Name	Last Name	Class 1	Composite key
Aman	Yadav	Science	Aman Yadav
Bhola	Singh	Chemistry	Bhola Singh
Aman	Singh	Social science	Aman Singh

In the above example, Both the First name column and Second name column can not identify each record separately, hence we can create a Composite Key by Combining First name and Second name as shown in the Composite key column, to create a unique identifier for each record.

Unique Key

This key in DBMS is a column or set of columns that ensure that each value in the column is unique and not repeated.

They prevent duplicate values in a column. They are very similar to the primary keys but the only difference is that there can be more than one unique key in a table, but the primary key is only one.

Unique keys can also uniquely identify the value in each row of a table and have different values in each row without being a Key Identifier. For better understanding let’s understand it with an example:

Student ID	Student name	Class 1	Class 2
001	A	Science	English
002	B	Chemistry	Maths
003	C	Social science	Social Science

In the above example, Student ID is the Primary Key, Student Name can also identify each record uniquely and has different values in each column, hence Student Name can be chosen as Unique Key.

Next Step

If you find the above information useful and you want to learn more about this topic I recommend you to please check the Data Analytics Course facilitated by Henry Harvin Education, Henry Harvin Education is amongst the leading E-learning Platforms in the world, The Institute has 1200+ courses across more than 37 categories.

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Conclusion

A database is a set of data, in which data is represented through various tables, and  Keys in DBMS help establish relationships between different tables in a database. By establishing relationships between different tables we can ensure Zero duplicates and prevent redundant data from entering our database, this makes data more manageable and easy to retrieve relevant data as and when required.

Also Read:

• What are the Keys in DBMS? Different Types of Keys
• Data Science Blog Henry Harvin Education
• Functional Dependency in DBMS
• What are Keys in DBMS? Different Types of Keys

Frequently Asked Questions What is a Key in DBMS?

Q.1 Keys in DBMS are like special labels for identifying each row in a table uniquely.

Ans. Databases are huge and there is always some possibility of duplication due to the large quantity of data, and different keys in DBMS resolve this issue by establishing relationships between different tables by providing a unique identifier. 

Q.2 What is the Foreign key in DBMS?

Ans.The foreign key in DBMS is an attribute that establishes the relationship between two or more tables in a way that ensures that the value entered in the foreign key column exists in the primary key column in the referenced table, By accurately representing table relationship it makes data quiring and data revival easy and efficient.

Q.3 How many types of Keys exist in DBMS?

Ans. There are 7 types of Keys in DBMS:

1. Primary Key
2. Candidate Key
3. Super Key
4. Foreign Key
5. Composite Key
6. Alternate Key
7. Unique Key  

Q.4 What is the difference between Candidate and super key?

Ans. The main difference between Candidate and Super keys is 

• All candidate keys are super keys, but not all the super keys are candidate keys.
• Sepur keys may sometimes contain data not necessary to uniquely identify, whereas Candidates are the contenders for the Primary key but are not chosen.

Q.5 Why Keys are required in DBMS?

Ans. Database represents a large collection of records and Keys in DBMS are like special labels for identifying each row in a table. Databases are huge and there is always some possibility of duplication due to the large quantity of data, and different keys in DBMS resolve this issue by establishing relationships between different tables by providing a unique identifier. 

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