Is AB a candidate key of this relation?

Is AB a candidate key of this relation?

Yes, ABD is a candidate key. No subset of its attributes is a key. 6. Consider a relation with schema R(A,B,C,D) and FDs {AB -> C, C -> D, D -> A}.

Is there any way to check whether a relation has only one candidate key or more than one candidate keys justify your answer by giving proper examples?

For any given relation, It is possible to have multiple candidate keys. There exists no general formula to find the total number of candidate keys of a given relation.

How do I find candidate keys for a relation?

1. The first step in the process of finding a normal form and decomposing a relation is to find the candidate. keys.
2. R = (ABCDE), F = {A -> C, E -> D, B -> C}
3. R = ABCDE, F = {A -> BE, C -> BE, B -> D}
4. R = ABCDEF, F = {A -> B, B -> D, C -> D, E -> F}
5. R = ABCD, F={AB -> C, BC -> D, CD -> A}
6. R = ABCD, F={A -> BCD, C -> A}

What are the possible candidate keys of this relation?

Candidate Key is minimal set of attributes of a relation which can be used to identify a tuple uniquely. For Example, each tuple of EMPLOYEE relation given in Table 1 can be uniquely identified by E-ID and it is minimal as well. So it will be Candidate key of the relation.

Can a relation have no candidate key?

A candidate key, or simply a key, of a relational database is a minimal superkey. Every relation without NULL values will have at least one candidate key: Since there cannot be duplicate rows, the set of all columns is a superkey, and if that isn’t minimal, some subset of that will be minimal.

Is primary key subset of candidate key?

Candidate keys are a subset of Super keys. Primary key is a Candidate key chosen to uniquely identify tuples in the table. Primary key values should be unique and non-null. There can be multiple Super keys and Candidate keys in a table, but there can be only one Primary key in a table.

Can a candidate key be null?

Candidate key column can have null value. Primary key is most important part of any relation or table.

How many candidate keys can a relation have?

one candidate key
There can be more than one candidate key in a relation. For Example, STUD_NO is the candidate key for relation STUDENT. The candidate key can be simple (having only one attribute) or composite as well.

Is it always possible to have multiple candidate keys?

There can be multiple candidate keys in a database relation and each candidate can work as a primary key for the table. Primary Key – A primary key is a column or a set of columns that identifies some record uniquely. Only one candidate key can qualify as the primary key.

What is the key of R?

Since, closure of AD contains only all the attributes of R, hence AD is candidate key. Since closure of BC contains only all the attributes of R, hence BC is candidate key. Since the closure of CD contains only all the attributes of R, hence CD is candidate key.