In Database management systems (DBMS), a candidate key refers to a collection of one or more columns that possess the capability to uniquely identify a specific row within a table. It is commonly referred to as a “unique identifier” or “primary key.” In this guide let’s explore what is Candidate keys in DBMS, its major types and how to choose ethe right key while designing a database.
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What are Candidate Keys
Candidate keys are essential in Database Management Systems (DBMS) as they support the structure of a database. They uniquely identify each record and allow for data integrity within tables. This article will explore what constitutes a candidate key and how it is used in database design. We will also discuss the different types of candidate keys and their importance to database structures. Understanding these concepts allows you to maximize your databases’ efficiency while ensuring data integrity.
Creating a Candidate Key
Here’s a syntax example of how a candidate key can be defined in a typical database management system (DBMS):
table_name is the name of the table where the candidate key is being defined.
column1, column2, column3, and so on, represent the columns that make up the candidate key.
candidate_key_name is an optional identifier for the candidate key constraint. It can be any meaningful name you choose.
PRIMARY KEY is the constraint that indicates that the specified columns form a candidate key. It enforces uniqueness and provides fast access to the data.
By specifying the PRIMARY KEY constraint on the columns, you are declaring them as a candidate key for the table. This ensures that the combination of values in those columns will be unique for each row in the table.
Characteristics of a Candidate Key
A candidate key is a set of columns within a table that can be used to identify each record uniquely. A candidate key must meet the following criteria:
Uniqueness
All the values in the candidate key must be unique, meaning no two records in the table have the same combination of values for those attributes.
Non-redundancy
All the attributes in the candidate key must be necessary for uniquely identifying each record. This means that no attribute can be removed without losing the ability to differentiate between two records.
Non-nullability
Every attribute in a candidate key must contain a value that is not NULL (missing data).
Irreducibility
Once the candidate key in DBMS has been formed, it should not be possible to reduce its size by removing any attributes.
Significance of Candidate Keys in Database Design
The primary purpose of a candidate key is to provide a unique identifier for each record in a table, which helps ensure data integrity and accuracy. In addition, candidate keys in DBMS can even be used to create relationships between tables and simplify query language operations on the database.
Furthermore, a Business Analytics course can help further your understanding of databases and candidate keys. You can learn how to design efficient databases, query them effectively, and identify relationships within the data.
Understanding the Key Concepts with Examples
Lets look at the types of candidate key in detail to understand the difference.
Type of Candidate Key
Description
Example
Single Attribute
Contains a single attribute used as the primary key
Student ID Number (e.g., 123456)
Composite
Contains multiple attributes and is formed by combining them. This type of key can identify records uniquely within one table or across different tables in the database
First Name + Last Name (e.g., John Smith)
Natural
Uses data from the table, such as customer IDs, employee numbers, etc., which are already unique for each record
Employee Number (e.g., EMP-123456)
Artificial/Surrogate
Uses an exceptional value the database generates, such as an auto-incrementing number or UUID. This essential type is often used for tables with no natural candidate keys
Auto-Incrementing ID (E.g., 1,2,3…)
Types of Candidate Keys
Primary candidate keys
Primary candidate keys in DBMS are the main type of candidate key used in database design. They are typically single attribute or composite keys that use two or more features to identify each record within a table uniquely. Examples of primary candidate keys include student ID numbers, employee numbers, and unique customer IDs.
Alternate (or Secondary) Keys
Alternate (or secondary) keys are additional sets of columns that can identify records within a table. These types of keys are often created as backup options in case the primary key fails or is unsuitable for a given situation. For example, a table may have an employee number as the primary key, but it may also have an email address column that can act as a secondary key.
Composite candidate keys
Composite candidate keys in DBMS are formed by combining two or more columns from the same table. This type of key is used when there is no single column that can be used to uniquely identify each record—for example, if two people have the same name but different last names. By combining first and last names into a composite key, you can ensure each record has a unique identifier. Other examples include student ID numbers combined with birth dates or ISBN codes combined with book titles.
How to Select Candidate Keys in DBMS
When selecting a candidate key in DBMS, you should consider the type of data stored in the table and how it will be used. A primary key should always serve as a unique identifier for each record in the table, but there are other factors to consider. Suppose your database will store personal records such as customer information or employee data. In that case, you may want to use natural keys such as ID numbers or social security numbers since these values are already unique for each person.
A foreign-key constraint can also be added to the database, which ensures that any values used in a foreign key column must exist in the primary key of the referenced table.
Concept of Normalization and its Relationship with Candidate Keys
Normalization is an essential concept in database design. It refers to organizing data into separate related tables and ensuring that each table contains only one type of data. Normalization helps reduce redundancy and improve data integrity by eliminating duplicate information.
By knowing Data Warehousing and Data Mining, you can also learn how to normalize a database and choose the right candidate keys. Candidate keys are an essential part of normalization and can be used to create relationships between tables.
Differentiate Between Candidate Keys, Primary Keys, and Foreign Keys
Let’s deep dive to understand the major difference between Candidate Keys, Primary Keys, and Foreign Keys in detail.
Feature
Candidate keys
Primary keys
Foreign keys
Definition
A candidate key is a set of columns that uniquely identifies every record in a database table
A primary key is a combination of attributes, or an attribute uniquely identifying each table record.
A foreign key is an attribute/combination of attributes in one (referencing) table that refers to the primary key in another (referenced) table
Purpose
Used to ensure data integrity and accuracy by identifying each record uniquely
Used to enforce relationships between different tables and used for implementing referential integrity within the database
Used to ensure data integrity and accuracy by identifying each record uniquely
Example
Student ID numbers, employee numbers, unique customer codes
ID numbers, email addresses, social security numbers
combination of primary keys from two different tables
What are Composite Candidate Keys in DBMS
Composite candidate keys in DBMS are formed by combining two or more columns from the same table. This type of key is used when there is no single column that can be used to uniquely identify each record—for example, if two people have the same name but different last names. By combining first and last names into a composite key, you can ensure each record has a unique identifier.
Best Practices for Designing Candidate Keys
When designing candidate keys, it’s essential to consider all the criteria for valid keys—uniqueness, non-redundancy, non-nullability, and irreducibility.
Additionally, you should choose a type of key that best fits your needs—whether a single attribute, composite, natural, or artificial/surrogate key. When selecting a primary or alternate key for your database design, look at the data stored in the table and how it will be used to determine which type of crucial best suits your needs.
Ensuring Data Integrity with Candidate Keys
Candidate keys in DBMS are essential to database design as they help ensure data integrity and accuracy by providing each record is uniquely identified. When designing candidate keys, it’s critical to consider all the criteria for valid keys and choose a type of key that fits your needs—whether it be a single attribute, composite, natural, or artificial/surrogate key.
Choosing the Right Candidate Key
Choosing the right candidate key for a database is essential to ensure data integrity and accuracy. When selecting Primary keys in DBMS or an alternate key, it’s vital to consider all the following criteria for valid keys
Uniqueness – The key should be unique, and it should be not subject to change.
Non-nullability – The keys cannot be nullable.
Irreducibility – The keys should be impossible to transform into or restore to a desired or simpler condition.
Stability – The key should not change over time.
Conclusion
Candidate keys in DBMS are an essential part of database design, as they help ensure data integrity and accuracy by providing each record is uniquely identified. Normalization also requires the use of candidate keys to create relationships between tables. When designing candidate keys, it’s important to consider all the criteria for valid keys and choose a type that fits your needs. By understanding these concepts and following best practices for designing candidate keys, you can maximize the efficiency of your databases while ensuring data integrity.
FAQs
Why do we need Candidate Keys in DBMS?
Candidate keys are essential in a database management system (DBMS) because they provide a means to uniquely identify each row within a table. They ensure data integrity by preventing duplicate records and enable efficient data retrieval operations by serving as primary keys. Candidate keys play a vital role in maintaining the consistency of a database and establishing relationships between tables through foreign keys.
What are composite candidate keys, and in what situations are they useful?
Composite candidate keys in DBMS are formed by combining two or more columns from the same table. This type of key is used when there is no single column that can be used to uniquely identify each record—for example, if two people have the same name but different last names.
How do candidate keys contribute to data integrity in a database?
Candidate keys in DBMS are an essential part of database design, as they help ensure data integrity and accuracy by ensuring each record is uniquely identified.
Why do we Need a Candidate Key?
A candidate key is needed to ensure data integrity and accuracy. Using a candidate key for these types of relationships ensures that only valid records are stored in your database.
Can candidate keys be modified or updated in a database?
Yes, candidate keys in DBMS can be modified or updated in a database. However, it is crucial to consider any changes' implications - any modifications should not create data integrity issues or duplicated records.
