The main difference between super key and candidate key is that the super key is a set of one or more attributes that can uniquely identify a record in a table, while the candidate key is a super key that does not contain any redundant attributes.
Generally, DBMS is a software that helps to store and manage data in the databases. A Relational DBMS (RDBMS) is a DBMS created according to the relational model. For example, MySQL, MSSQL are some common RDBMS. Moreover, there are multiple tables in a single database. Keys help to connect the tables of a database. Moreover, they help to understand the data and make them more meaningful. Overall, there are various types of keys; two of them are super key and candidate key.
Key Areas Covered
1. What is Super Key
-Definition, Functionality
2. What is Candidate Key
-Definition, Functionality
3. Difference Between Super Key and Candidate Key
-Comparison of key differences
Key Terms
Candidate Key, Super Key
What is Super Key
Super key is a key that consists of one or more attributes which can uniquely identify a row in a table. A super key is a superset of a candidate key.
For example, assume a table called student. It has three columns: id, name, and phone. We can use id to identify each row uniquely. Consider the combination of id and name. Two students can have the same name, but their ids will be different. Therefore, we can use both id and name combination to identify each record separately. Similarly, each student will have their own phone numbers. So, we can use it to identify each row separately. Therefore, id, id and name, phone are super keys.
What is Candidate Key
A candidate key is a key selected from the set of super keys. A candidate does not have any redundant attributes. Generally, a candidate key does not have null or empty values and consists of one or many attributes. Moreover, there can be more than one candidate keys for a table. According to the above-mentioned student table, the id and phone do not have any redundant attributes. Therefore, these are candidate keys of the table.
Difference Between Super Key and Candidate Key
Definition
A super key is a set of one or more attributes that can uniquely identify a row in a table. But, a candidate key is a super key with no redundant attributes. Thus, this is the main difference between super key and candidate key.
Dependency
Moreover, super keys do not depend on other keys, while all candidate keys are super keys. Hence, this is another difference between super key and candidate key.
Examples
In a student table with columns id, name and phone, the super keys are id, id and name, phone. On the other hand, id, phone are the candidate keys.
Conclusion
In RDBMS, keys help to connect the data in different tables of the database. Those keys represent the relationship between multiple tables. Therefore, it makes the data more useful. In brief, two types of keys are super key and candidate key. The main difference between super key and candidate key is that super key is a set of one or more attributes which can uniquely identify a record in a table while candidate key is a super key which does not contain any redundant attributes.
References:
1.Singh, Chaitanya, et al. “Super Key in DBMS.” Beginnersbook.com, 11 Dec. 2018, Available here.
2.Singh, Chaitanya, et al. “Candidate Key in DBMS.” Beginnersbook.com, 11 Dec. 2018, Available here.
3.“Introduction to Database Keys.” Studytonight, Available here.
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