Introduction
In database management systems, key comprehension is crucial to designing efficient and effective databases. Among various types of keys, candidates’ keys are of important importance. A minimal superkey that identifies exclusively tupels in a relationship is called a candidate key. This article will explore the idea of candidates, including their characteristics, importance and ways in which they vary from other types of SGBM keys.
Overview
- Understand the definition and properties of the candidates’ keys.
- Identify the importance of candidates’ keys in database design.
- Make a distinction between super keys, foreign keys, candidate keys and primary keys.
- Discover how to locate potential keys within a relationship.
What is a candidate keys?
A candidate key is a set of one or more attributes that can exclusively identify a tuple in a relationship. Each candidate key has the following properties:
- Singularity: There are no two different tuples in a relationship may have the same value for the candidate’s key.
- Minimality: There is no suitable subset of the candidate’s key has the property of uniqueness.
In simpler terms, a candidate key is a minimal superkey without redundant attributes.
Properties of candidates’ keys
Understand the properties of candidates’ keys helps in their identification and application:
- Singularity: Ensures that each tuple in a relationship is exclusively identifiable.
- Minimality: Guarantee that the singularity property of the candidate’s key cannot be lost by eliminating any attribute.
- Not null: Candidates’ keys cannot contain null values as they must exclusively identify tuple.
- Immutability: The value of a candidate key should not change over time to maintain data integrity.
Importance of Candidates Keys in SGBM
Candidates’ keys are essential in designing database design for various reasons:
- Data integrity: They ensure that each database record is unique and identifiable.
- Normalization: By reducing redundancy and improving data integrity, they help in the standardization process.
- Indexing: They are often used for indexing, which improves the efficiency of data recovery operations.
Candidate key vs. primary
A primary key is a special type of candidate key. Here’s how they differ:
- Primary key: A single candidate key chosen by the Database Designer to identify exclusively tupels in a relationship. Cannot contain null values.
- Candidate key: All potential keys that can identify exclusively tuple. There may be several candidate keys, but only a primary key.
Example
In the student table, both the student and the email could be candidates, but the student is chosen as the main key.
Candidate key vs. Super Key
A super key is a set of one or more attributes that can identify exclusively tuple in a relationship. The key difference between the Super Keys and the Candidate Keys is the minimum:
- Super Key: May contain additional attributes not required for singularity.
- Candidate key: A minimum superkey without redundant attributes.
Example
If Studentid is a candidate key, then the student, the name is a super key.
Here, Studentid is a candidate key and the student’s name, the name is a super key.
Candidate key vs. foreign key
A foreign key is an attribute or set of attributes in a table that exclusively identifies a row of another table or the same table. Here is the distinction:
- Candidate key: Identifically identifies tupels within your own table.
- Foreign key: It allows the referential integrity between two tables connecting the foreign key and the primary key of a table.
Example
Consider two tables, student and enrollment:
Student Table:
| Studentid (Primary Key) | Name |
|---|---|
| 1 | Alice |
| 2 | Bob |
Enrollment Table:
| Registered | Studentid (Foreign Key) | Course |
|---|---|---|
| 101 | 1 | Mathematics |
| 102 | 2 | Science |
In this case, the student in the student database is referenced by Studentid in the registration table, which is a foreign key.
How to identify the keys of the candidates?
The identification of the candidate’s keys involves the following steps:
- List all attributes: List all attributes of the relationship.
- Determine all possible combinations: Consider all possible combinations of attributes.
- Check the singularity: Identify what combinations they identify exclusively the tupes.
- Please ensure at least: Remove combinations containing redundant attributes.
Example
Consider a student of Relationship with Studentid attributes, name, email and phonenumber.
- List all attributes: Student, Name, Email, Phonenmer
- Determine all possible combinations: {STUDENTID}, {E -MAIL}, {PHONENUMBER}, {STUDENTID, NAME}, etc.
- Check the singularity: Studentid and e -mail identify exclusively tupes.
- Please ensure at least: The student and email are minimal and therefore the candidate keys.
Examples and use cases
Now we will examine the examples and use cases of candidate key.
Example 1: Table of Employees
In this table, the employee and the email are candidate key.
Example 2: Product Table
| Production | ProductName | Serialnumber |
|---|---|---|
| P001 | Portable | SN12345 |
| P | Smartphone | SN67890 |
In this table, Productid and Serialnumber are candidates.
Conclusion
The efficiency and integrity of a database are largely dependent on their candidate keys. They are essential for indexing, the normalization of the databases and maintenance of the integrity of the data as they provide the tupes with a unique identity. Database designers can greatly improve the speed and trust of their databases by correcting and properly applying the candidate’s keys.
Frequent questions
A. Yes, a table may have several candidate keys, but only one of them is the main key.
A. No, the candidate keys must be no null to ensure that they identify exclusively tuple.
A. A primary key is a candidate key chosen by the database designer to identify exclusively tuple. All the primary keys are the keys of the candidates, but not all the keys of the candidates are the primary keys.
A. The keys of the candidates help standardization by identifying unique records and eliminating redundancy, thus improving the integrity and consistency of data.
A. No, a foreign key refers to a main key in another table to maintain referential integrity. Do not exclusively identify tupels within your own table.
My name is Ayushi Trivedi. I’m a B. Tech graduate. I have 3 years of experience working as an educator and content editor. I have worked with several Python libraries, such as Numpy, Pandas, Seaborn, Matlotlib, Scikit, Imblearn, Linear Retusion and many more. I am also the author. My first book called #Turning25 has been published and is available on Amazon and Flipkart. Here, I am editor of technical content in Analytics Vidhya. I am proud and happy to be avian. I have a great team to work with. I love building the bridge between technology and student.
