Define the following: Primary key, Candidate key, Alternate key, Foreign key

Q. Define the following:

(a) Primary key

(b) Candidate key

(c) Alternate key

(d) Foreign key

Answer :-

(a) Primary key :- A Primary Key is a set of one or more attributes that can uniquely identify tuples within the relation.

(b) Candidate key :- All attribute combinations inside a relation that can serve as primary key are Candidate Keys as they are candidates for the primary key position.

(c) Alternate key :- A candidate key that is not the primary key is called an Alternate Key.

(d) Foreign key :- A non-key attribute, whose values are derived from the primary key of some other table, is known as Foreign Key in its current table.