Last Updated on July 10, 2023 by Mayank Dham
What are Keys?
Keys in DBMS are attributes or combinations of attributes that are used to uniquely identify records within a database table. They play a crucial role in maintaining data integrity and enabling efficient retrieval and manipulation of data.
Types of keys in DBMS
- Primary Key: A primary key is a unique identifier for each record in a table. It ensures that no two records in the table have the same key value. Every table in a database should have a primary key, and it is used to enforce entity integrity.
- Candidate Key: A candidate key is an attribute or combination of attributes that can be used as a primary key. It satisfies the uniqueness and non-null property.
- Foreign Key: A foreign key is an attribute or combination of attributes in one table that refers to the primary key of another table. It establishes a relationship between the two tables and maintains referential integrity.
- Super Key: A super key is a set of one or more attributes that can uniquely identify a record within a table. It may contain more attributes than necessary to uniquely identify a record.
- Unique Key: A unique key is a key that ensures the uniqueness of values in a column or combination of columns. Unlike the primary key, it allows null values.
- Alternate Key: An alternate key is a candidate key that is not chosen as the primary key. It provides an alternative option for uniquely identifying records.
What is Super Key in DBMS?
In database management systems (DBMS), a super key is a set of one or more attributes (columns) that can uniquely identify a record (row) within a table. It is a broader concept than the primary key and can include additional attributes beyond what is required for uniqueness.
A super key satisfies the uniqueness property, meaning that no two records in the table can have the same combination of attribute values within the super key. However, it may contain more attributes than necessary to uniquely identify a record. Therefore, a super key can have redundant or extraneous attributes.
Example of Super Key in DBMS
In a database where customer orders and purchased products are stored, the super key could be a composite key consisting of the customer ID and product ID. This combination guarantees the unique identification of each customer order based on the products they have purchased.
Another instance could involve a database recording customer orders, including order number, customer name, and order date. In this case, the super key could be formed by combining the order number and order date, ensuring the unique identification of each order.
In summary, a super key in a database management system (DBMS) is a set of one or more attributes that can uniquely identify a record within a table. It satisfies the uniqueness property but may contain additional attributes beyond what is required for uniqueness. Super keys are important during the database design phase for identifying potential candidate keys, from which the primary key is chosen. They serve as a foundation for establishing relationships, enforcing data integrity, and optimizing database operations.
Frequently Asked Questions (FAQs) Related Super Key in DBMS
Below are some Frequently asked questions related to Super key in DBMS:
Q1. Why is a super key important in DBMS?
Super keys play a crucial role in database design and integrity. They help identify potential candidate keys and establish relationships between tables. Super keys also enable efficient retrieval and manipulation of data in a database.
Q2. How is a super key different from a primary key?
A super key is a set of attributes that can uniquely identify a record, while a primary key is the chosen key among the super keys to uniquely identify records within a table. The primary key is unique, non-null, and used to enforce entity integrity.
Q3. Can a super key have redundant attributes?
Yes, a super key can have redundant attributes, meaning it may contain more attributes than necessary to uniquely identify a record. Redundant attributes do not affect uniqueness but may result in inefficient storage and processing.
Q4. What is the difference between a super key and a candidate key?
A super key is a set of attributes that uniquely identifies a record, whereas a candidate key is a super key without any redundant attributes. Candidate keys are the potential choices for a primary key.
Q5. Can a table have multiple super keys?
Yes, a table can have multiple super keys. Each super key represents a different combination of attributes that can uniquely identify records within the table. However, only one of them is typically chosen as the primary key.
Q6. Is a foreign key a type of super key?
No, a foreign key is not a type of super key. A foreign key is an attribute or combination of attributes in one table that refers to the primary key of another table. It establishes relationships between tables, while a super key uniquely identifies records within a single table.