Solution

The correct answer is A candidate key for which no proper subset is also a candidate key is called a super key.

Key Points

A candidate key for which no proper subset is also a candidate key is called a super key. This statement is incorrect because a candidate key is a minimal set of one or more attributes that can uniquely identify records in the entity set, and for a candidate key, no proper subset of it is a candidate key. However, this does not make it a super key. A super key is a set of one or more attributes that can uniquely identify records, but it may not be minimal. That is, a super key has a property that some subsets of it are still super keys.

Additional Information

•  Super Key: A super key is a set, or any subset of, one or more columns (attributes) that can be used to uniquely identify a record in a database table. It can include extraneous attributes.
• Candidate Key: A candidate key is a minimal set of columns (that is, a super key reduced to its irreducible minimum) which can uniquely identify a record. There can be more than one candidate key, but they each must be able to uniquely identify a record without any extraneous data.
• Primary Key: The primary key is a distinct type of candidate key chosen by the database designer to make a row unique in a table. It can neither have null values nor duplicate values.
• Foreign Key: A foreign key in a database is a field or collection of fields in one table, that is a primary key in another, related table. The purpose of the foreign key is to ensure referential integrity of the data.