In context of a relation in database, choose a false statement:

Question

Accepted Answer

The correct option is (4):
The statement "Primary key is obtained by removing one or more attributes from a candidate key" is fundamentally false in the context of relational database theory. A **Candidate Key** is defined as a *minimal* Super Key—meaning it contains the fewest attributes necessary to uniquely identify a tuple. If you remove any attribute from a Candidate Key, it loses its minimality property and, crucially, its uniqueness property, meaning it can no longer uniquely identify a row. The **Primary Key** is simply one of the available Candidate Keys chosen by the database designer, not a reduced version of one.

The incorrect option is (1):
This statement, "There can be more than one super keys," is absolutely true. A **Super Key** is any attribute or set of attributes that uniquely identifies a row in a table. Since adding any non-key attribute to an existing Super Key still preserves the ability to uniquely identify the row, a single relation can and usually does have multiple Super Keys. For instance, if {ID} is a Super Key, then {ID, Name} is also a Super Key.

The incorrect option is (2):
The statement "A candidate key is a minimal super key" is the formal definition of a **Candidate Key** and is therefore true. The term 'minimal' is key here; it means that no proper subset of the Candidate Key can also function as a Super Key. This minimality constraint ensures that Candidate Keys are non-redundant identifiers, containing only the attributes strictly required for unique identification.

The incorrect option is (3):
This statement, "One of the candidate keys is designated as primary key," is also true. A relation can often have several sets of attributes that qualify as Candidate Keys. The database designer's task is to select one of these keys—the one considered most stable, simple, and practical—to be the table's official **Primary Key**. The Candidate Keys not selected become the **Alternate Keys**.