What is super key in DBMS?

Super key is the combination one and more attribute to uniquely identify a tuple. For example, we have a student table with attribute (stu_rollno., stu_name, stu_add, stu_branch, stu_Aadharno.)

Here we can have several sets of a superkey as given below.

stu_rollno. + stu_name
stu_rollno. + stu_name + stu_branch
stu_Aadharno. + stu_name
stu_rollno. + Stu_Aadhar
stu_Aadharno. + stu_name + stu_branch
stu_rollno. + stu_name + stu_add

These were a few combinations of superkey that can identify the tuple value obsoletely.

However, stu_rollno. and stu_Aadharno is also a candidate key which is also capable to fetch the tuple value uniquely. So stu_rollno. and stu_Aadhar will be a minimal superkey which can easily identify the whole tuple value.

See, below another example for the same.

SuperKey Example

So, here we can say that super is key is the strong combination of attributes that which provide a guarantee to provide the unique tuple value.

Super key is different from the composite key. If in a case we don’t have any candidate key in our relationship then the combination of a possible attribute which can uniquely identify a tuple value is known as a comosite key.


Super key is the strong key which assures a guarantee to identify the tuple uniquely. Let’s have a relation with one candidate key with some other attributes which are not a key. Then a super key can be all possible combination of candidate key with the other attributes of the relation.

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What is a candidate key in DBMS?

An attribute or a column in a table that can identify a full tuple or row records in a data table is considered as a candidate key.

Now the question is that all the other keys like primary, alternate, super, unique, foreign also used to uniquely identify a tuple value so are they all a candidate key?

Yes, any key that is capable to identify a tuple value is considered as a candidate key though they could also have their own features like a primary key does not allow to enter a null value. Whereas unique key allows doing the same.


In a very simple language, we can say that a candidate key is a generalized concept to have unique value to identify the whole row record. thus any DBMS key fulfilling this criterion will be a candidate key.


Every key that can easily identify a tuple value with the property of uniqueness, mean to say that every tuple has a unique value for a particular attribute value is called a candidate key. There may be one and more candidate key in the database table.

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What is Key in DBMS?

Hello Friends,

In this blog post, I will let you know about one of the most important and interesting topics of a database that is KEY.

While reading the same subject or sometimes having relevancy with the technology you would have heard about this technical word key if not exactly the same then you would have heard like a primary key or foreign key.

So those who have been studying the database or have studied should know this technical word key and all further classification related to this word key.

Like its name key which is useful in opening a lock in our real life, it is used to find the particular tuple and attribute information in relation in DBMS.

In the database we have a table, in a table, we have several rows and column. Here key can be a particular column or attribute value which is used to identify whole row or tuple value.

A column which is made a key will have a unique value in all the row. On this basis, we can say that an attribute which uniquely identifies a tuple value is known as a key.

There are several types of keys in the database which are given below.


Candidate key: Unique tuple value for each attribute.
Primary key: uniquely identify a tuple, does allow null.
Foreign key: Help to access other table data.
Unique key: Uniquely identify tuple, allow null value.
Super key: composite key identify a tuple value. a minimal superkey is candidate key.
Alternate key: Uniquely identify the tuple value but not a primary key.

I will discuss each of these above-given keys one by one in detail in my upcoming blog.


You should be confused with a key in the database. it is simply a column which has a unique value in each row and on the basis of this value we fetch the detail of a particular row. We may fetch one or more row result with the help of this key and can show the result as per our requirement.

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