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

Question

Question

This question was previously asked in

HTET PGT Official Computer Science Paper - 2019

There can be more than one super keys.
A candidate key is a minimal super key.
One of the candidate keys is designated as primary key.
Primary key is obtained by removing one or more attributes from a candidate key.

Answer 1

Super Key

It is an attribute (or set of attributes) that is used to uniquely identifies all attributes in a relation.
All super keys can’t be candidate keys but its reverse is true.
There can be more than one super key.
In relation, the number of super keys is always greater than or equal to the number of candidate keys.
There always exists at least one super key in a table.

Candidate key

It is a minimal set of attributes necessary to identify a tuple; this is also called a minimal super key.
Candidate key can be more than one.
One of the candidate keys is designated as the primary key.

Primary key

Candidate key from the table selected by the database administrator to uniquely identify tuples in a table known as the primary key.
Since the candidate is a minimal set of attributes necessary to identify a tuple therefore the primary key is also a minimal set of attributes necessary to identify a tuple and hence primary key cannot be obtained by removing one or more attributes from a candidate key.

Therefore option 4 is false