Exploring Candidate Keys in Database Design

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.

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):

CREATE TABLE table_name (
    column1 data_type,
    column2 data_type,
    column3 data_type,
    ...
    CONSTRAINT candidate_key_name PRIMARY KEY (column1, column2, column3, ...)
);

In the above syntax:

• 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.

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.

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.