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A superkey is defined as a set of attributes of a relation for which it holds that in all relations assigned to

that variable there are no two distinct tuples (rows) that have the same values for the attributes in this set.

As an example

Code:

Roll Number | First Name | Last Name

CSU0001 | Shabbir | Bhimani |

CSU0002 | SomeName | SurName |

CSU0003 | Larry | page |

Now here we have the following as super keys

1. Roll Number | First Name

2. Roll Number | First Name | Last Name

Now in plain language Any Unique key with some Non Unique key combination is called a super key of the

relationship.

A candidate key of a relationship is a set of attributes of that relationship such that there are no two distinct

tuples with the same values for these attributes. In simple example candidate key is a minimal superkey, i.e. a

superkey of which no proper subset is also a superkey.

Since a relation is a set(no duplicate elements), it holds that every relation will have at least one candidate key

(because the entire heading is always a superkey). For practical reasons RDBMSs usually require that for each

relation one of its candidate keys is declared as the primary key

Quote:

For example, Given an employee table consisting of the columns:

employeeID

name

job and

departmentID

we could use the employeeID in combination with any or all other columns of this table to uniquely identify a row

in the table. Examples of superkeys in this table would be {employeeID, Name}, {employeeID, Name, job}, and

{employeeID, Name, job, departmentID}.

In a real database we don't need values for all of those columns to identify a row. We only need, per our example,

the set {employeeID}. This is a minimal superkey - that is, a minimal set of columns that can be used to identify a

single row. So, employeeID is a candidate key.

Now, if employeeID is a candidate key then why not it is the superkey. Because employeeID can also uniquely

identify the tuples.

(2) In your example why Roll number is not the superkey as it is uniquely identifying the tuples?

(3)

Quote:

Any Unique key with some Non Unique key combination is called a super key of the relationship

Is it necessary that Unique key has to be combined with some Non Unique key to be called as a super key.

Unique key is also a super key but the minimal super key is called candidate key and all candidate keys are super

keys but the reverse is not true.

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βˆ™ 2011-09-13 20:11:32
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Q: What are the difference between superkey and candidate key?
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Difference between super key and candidate key?

Candidate key - A candidate key is a field or combination of fields that can act as a primary key field for that table to uniquely identify each record in that table. Superkey - A superkey is defined in the relational model as a set of attributes of a relation variable (relvar) for which it holds that in all relations assigned to that variable there are no two distinct tuples (rows) that have the same values for the attributes in this set. Equivalently a superkey can also be defined as a set of attributes of a relvar upon which all attributes of the relvar are functionally dependent.


Is super set of the super key is the super key.?

A superkey is essentially a super set of a key. Consider a relation R(a,b,c,d) where {a} is the key. Any addition to a such as {a,b},{a,c}, {a,b,c} are considered superkeys. Furthermore, if you add more attributes to a superkey, it will be considered a superkey as well. So yes, a superset of a superkey is another superkey.


What is the prime attribute in DBMS?

prime attributes are the attributes of a candidate key which will give uniqueness. a candidate key is (the subset of superkey) which gives uniqueness. Super key is the maximum set of attributes that can provide uniqueness example ABCDE is a super key AB CD DE are the candidate keys s.t. AB is the primary key. CD and DE are the secondary/alternate keys.


What is difference between primary candidate and candidate key?

don't ask me I'm trying to find out to but i think it has something to do with the government


Difference between a super key and a candidate key?

Super Key : A Super key is a combination of attributes that can be uniquely used to identify a database record. A table might have many super keys. Candidate Key : A Candidate key uniquely idnetifies rows in the table. Any of identified candidate keys can be used as primary key. Candidate keys are a special subset of superkeys that do not have extraneous information in them.


Definition of super key with example?

A superkey is a combination of attributes that can be uniquely used to identify a database record. A table might have many superkeys. Candidate keys are a special subset of superkeys that do not have any extraneous information in them.


What is the difference between a key and a superkey in DBMS?

I am supposing that key means primary key.Superkey is any subset of attributes that uniquely identifies the tuples of a relation. This subset need not be minimal, that is, one can remove some attributes from it and it is still uniquely identifying. If all redundant attributes are removed you get a subset what is called primary key.


All types of keys in database?

* Alternate key - An alternate key is any candidate key which is not selected to be the primary key * Candidate key - A candidate key is a field or combination of fields that can act as a primary key field for that table to uniquely identify each record in that table. * Compound key - compound key (also called a composite key or concatenated key) is a key that consists of 2 or more attributes. * Primary key - a primary key is a value that can be used to identify a unique row in a table. Attributes are associated with it. Examples of primary keys are Social Security numbers (associated to a specific person) or ISBNs (associated to a specific book). In the relational model of data, a primary key is a candidate key chosen as the main method of uniquely identifying a tuple in a relation. * Superkey - A superkey is defined in the relational model as a set of attributes of a relation variable (relvar) for which it holds that in all relations assigned to that variable there are no two distinct tuples (rows) that have the same values for the attributes in this set. Equivalently a superkey can also be defined as a set of attributes of a relvar upon which all attributes of the relvar are functionally dependent. * Foreign key - a foreign key (FK) is a field or group of fields in a database record that points to a key field or group of fields forming a key of another database record in some (usually different) table. Usually a foreign key in one table refers to the primary key (PK) of another table. This way references can be made to link information together and it is an essential part of database normalization


Candidate key and primary key differnece?

All Primary keys are definitely Candidate Keys. A Candidate key is one which can be used as a Primary key that is not null and unique. That is one of the candidate keys can be chosen as a primary key.A Candidate key is a Unique Key and it can be used to find out any particular Tuple (row) in a table. The following are the differences between A Candidate key and a Primary Key: 1) A Unique key can be null but not a Primary key 2) On a table we can have only 1 primary key but 'N' number of unique keys.


Difference between public key and private key cryptography?

difference between public key criptography and privare key criptography


What is the difference between a key and a legend?

There is no difference.


What is overlapping key DBMS?

Overlapping Key is a type of candidate key which occurs in BCNF (Boyce –Codd Normal Form).In the difference between 3NF and BCNF Example : A 3NF table which does not have multiple overlapping candidate keys is guaranteed to be in BCNF. Depending on what its functional dependencies are, a 3NF table with two or more overlapping candidate keys may or may not be in BCNF.

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