Super, Alternate, Candidate, Primary, Composite, Foreign Key in DBMS

Last modified on January 3rd, 2019 at 2:31 pm

Today, in this fresh new article, we will cover the following topics;

A key is a field that uniquely identifies a tuple in the relation. Key is used to sort the data.

Super key is used to identify an attribute or set of attributes uniquely within the relation. Super key is a generalize superset of candidate keys.

Candidate keys are the set of all those attributes that can be selected as a primary key.

The primary key is the most suitable key to select a primary key.

All those attributes that can be selected as the primary key but not selected as primary key are called alternate keys.

A composite key is a set of two or more attributes that are together selected as a composite key.

Table: Exams

In this example, RegistrationNo and RollNo are candidate keys. If we select RegistratinNo as the primary key then RollNo is alternate key.

If the primary key is on both RegistrationNo and RollNo then it represents a composite key.

A foreign key is the primary key of one table that is linked with the field of another table.

In the figure, two tables are connected with each other through the foreign key.

CustomerID in left table is foreign key for CustomerID in right table

Test Your Understandings

1.Key not selected as primary key is called ………..?

Answer - Click Here:

alternate key

2.Keys that can be selected as primary key are called ………..?

Answer - Click Here:

candidate keys

3. ………..key is used to link the two tables?

Answer - Click Here:

Foreign key

Topic Covered

Super, Alternate, Candidate, Primary, Composite, Foreign Key in DBMS.