Composite key: Composite key vs Super key?

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Within this blog post, we are going to let you know about the Composite key: Composite key vs Super key. A composite key is the combination of one or more attributes that can uniquely identify a tuple value.

For example: if a student relation has attribute student ID, student name, student class, student project ID. The data of this relation is given below|Composite key: Composite key vs Super key|

In this blog post(Composite key: Composite key vs Super key), we are going to cover What a composite key gives an example. How do you define a composite key? What is the difference between a primary key and a composite key?…

… What is a composite foreign key? Are Composite Keys bad? What is the composite key in the database? What is the composite key in SQL? Is a composite key a primary key? (Composite key: Composite key vs Super key).

What is a composite key to giving an example?

When the primary key has two or more attributes to identify the tuple values uniquely then this key is called a composite key.

How do you define a composite key?

When two or more columns are taken together to identify the whole records of a row then it is considered a composite key.

The combination of these attributes must identify the row records uniquely whereas composite key attributes may or may not identify the records uniquely.

What is the difference between a primary key and a composite key?

The primary key is the single column in the table which is capable of identifying the whole records uniquely.

The primary key value can never be null and we can not either modify or update the primary key value.

Whereas the composite key is just like a candidate key where two or more columns uniquely identify the whole tuple value.

Table: Student

student id	student name	student class	student project id
1	Ravi	9th	101
2	Rita	9th	102
1	Shyam	10th	103
3	Anil	11th	101

Here in the above table, we don’t have any unique column or candidate key that can uniquely identify the tuple value.

so, here we need to join two column values or attribute values to make a key that can easily identify the tuple in the above-given relation.

So, we make student ID and student the primary key of this table, and this primary key is also known as a composite key of this table.

What is the difference between the composite key and the super key?

If you will see the definition of a super key which says that the combination of one or more attributes uniquely identifies a tuple value is called a super key.

You will confuse it with the composite key definition which is just looking similar at one glance.

But it is not like this, there is a difference between the composite key and the super key.

In the super key, the combination attributes have at least one candidate key which could be a primary as well as a unique key.

But when we don’t have a candidate key in our table then we have to make a set of combined attributes which can easily identify a tuple uniquely.

And now this combined key is called a composite key.

A candidate key is also known as a minimal super key but in the case of the composite key, there is no candidate key in the table.

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Quick Q&A:

What is the difference between a key and a super key?

See, In database table keys are nothing but a single attribute or set of attributes that can uniquely identify the value of the tuple.

SQL key can have either a single column or a set of multiple columns.

A super key is a single key or group of multiple keys that are used to identify the value of the tuple uniquely.

A super key could have redundant attributes that might not be important for identifying tuples.

Is super key also known as composite key?

Any key whether it is primary key, candidate key, super key, unique key, or any other key can be considered as a composite key.

But In a composite key, there must always be two or more columns that could uniquely identify the records in a table.

So, in simple words, the composite key is the combination of two or more columns that can uniquely identify the values of the tuple in a table.

Now, we can conclude that a super key is a composite key if it consists of two or more columns.

What is called a super key?

A super key is a set of keys that can uniquely identify the rows or tuple data in a table.

Here the word ‘super’ indicates the priority of a key.

So, a super key is the superset of a key known as a candidate key.

Can the super key be NULL?

The attributes which are included in the super key can have null values.

And same with the candidate key whose attributes can also have null values.

What is the candidate key?

A candidate key is a single or a set of multiple keys that can identify the value of the tuple uniquely.

But In the case of super key you would have read the same definition, so are they both the same?

The answer is no and yes both, why?

The super key can have those attributes too which can not identify the tuples uniquely.

But in the candidate key, each attribute would be capable of identifying the tuple value.

So we call the candidate key a minimal super key or subset of the super key which does not have unnecessary attributes in it.

But in case all the attributes in the super key can identify the tuples uniquely then it can be called a super key.

What is the candidate key vs the primary key?

The primary key acts as a minimal super key.

Thus, there would be only one primary key in a relation.

On the other side, a relation can have multiple candidate keys.

However, the attributes in the candidate key may contain the NULL value that opposes the primary key in it.

Conclusion:

When we are in a situation where we are unable to identify a tuple value uniquely with the help of one single column or we don’t have a candidate key or primary key in our table then we need to combine more than one attribute or column to make a primary key which can fetch thee tuple result, this type of primary key is known as a composite key. We can say that the super key is also composite but there is some minor difference between them|Composite key: Composite key vs Super key|

Within this blog(Composite key: Composite key vs Super key), we have gone through What a composite key is giving an example. How do you define a composite key? What is the difference between a primary key and a composite key? What is a composite foreign key? Are Composite Keys bad? What is the composite key in the database? What is the composite key in SQL? Is a composite key a primary key? A composite key example is the composite key in SQL When to use a composite primary key.

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