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Questions tagged [candidate-key]

A key is a set of attributes that is irreducibly unique and non-nullable within a table. Irreducible means that all the attributes of the key are necessary to guarantee uniqueness - remove any one attribute and the uniqueness property would be lost. A key may consist of zero, one or more attributes and a relational table (relation variable) must have at least one key and may have more than one.

A key is a set of attributes that is irreducibly unique and non-nullable within a table. Irreducible means that all the attributes of the key are necessary to guarantee uniqueness - remove any one attribute and the uniqueness property would be lost. A key may consist of zero, one or more attributes and a relational table (relation variable) must have at least one key and may have more than one.

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How can I find candidate key using FD.S?

VW->XYZ, Z->W, Y->VW it is Funtional dependency relation S{V,W,X,Y,Z}. candidate key is 'Y'?? or another?? I have a question. Why Z->W break normal form? and what type is broken normal form?
analog_by
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What does the "minimality" mean in database candidate keys?

I was very confused by the idea given by my professor when studying about candidate key (but i feel sham to ask him :p ) "no component of K can be eliminated without destroying the uniqueness property --- minimality" And i searched…
Ice.Rain
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Differences between minimal key and candidate key?

I Have this R(A,B,C,D,E) which have FD's : A->B, CD->E, E->A, B->D for this question I am required to find the minimal keys for R. To which I think I have this calculated as CA, CB, CD or CE (all optional). second part of this question: R(A,B,C,D)…
JBarnes
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Find all candidate keys that consist of 3 attributes if any? Sample Midterm

This is a question from a sample midterm from my database course. The solution is not given to us for the midterm and i just wanted to ask if my solution is correct in any sense Consider the following relation T=(N,A,I,V,L,P,C,D) with the FD={N->AI…
Ahmed Zaidi
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Candidate keys SQL

hi am recently learning about SQL and keys. i am wondering if there is n attributes to a relation table how many possible Candidate keys would there be?
boredj
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Database - Functional Dependency and Candidate Keys

I have am having a big problem grasping my head around Functional Dependencies and Candidate keys. I'm currently doing a project where I have to identify 'two' candidate keys and can only have four functional dependencies. My whole relation…
KieranLowe
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Prime attributes of a relation in database

What are the prime attributes of relation R(A,B,C,D) with following dependencies: F={AB->C , C->D , D->A} options are: i) A,B,C ii) A,B,D iii) A,B,C,D iv) B,C,D According to me answer should be (iii) option but answer is option (ii) Can anyone…
user3564975
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Can a CK have a FK referencing to a CK in another table?

Can a CK have a FK referencing to a CK in another table? Department (Dept, Dept_name) Employee(RegNo, FirstName, LastName, BirthDate, Dept_fk, Salary, City) Dept_name is a CK of the Department table. Can Dept_fk be part of a CK (Dept_fk, FirstName,…
user2984887
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How to find all possible candidate keys from a set of superkeys?

The superkeys of one example look as follows: ABCF CDF ACDF BCDF ABCDF ABCEF CDEF ACDEF BCDEF ABCDEF The output that contains all possible candidate keys: ABCF CDF In the example above, how do you get the possible candidate keys output from that…
Panda Panda
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Superkeys of this relation

I am trying to find the superkeys of this relation, but I am having troubles finding out how many superkeys there are and exactly what they are. I figured out that the candidate keys were {A},{B},{C},{D}. Here is the…
Jordan Thornley
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Finding Candidate Keys / Superkeys

I am working on another question here and it asks for the candidate keys and the superkeys. I believe I have the correct candidate keys, but if someone could verify that would be great. I am also just having trouble finding superkeys. I don't…
Jordan Thornley
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Find the SuperKeys

I am doing some textbook exercises that ask to find out the candidate keys for relation R as well as the superkeys. I have solved for the candidate keys, but I am not sure how to solve for superkeys? I am just a bit confused. Here is the relation…
Jordan Thornley
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Are middle attributes on a relation schemma prime?

In a relation schema, if: an attribute appears only on the left side then it is prime. an attribute appears only on the right side then it is non-prime. But what happens when there are attributes in the middle? Are they prime if they are a subset…
Mauricio
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Is Composite key a candidate key

Is composite key a subset of a pool of candidate keys? If it is a subset then why there is a new terminology for composite key, if candidate key can also formed with multiple columns. Update Simple Key - A simple key is one that has only one…
Satz Narayanan
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Finding a candidate key of a relation and if it is 2nf or 3nf

I am having issues with my homework. My teacher did not teach me well at all and I really want to learn how to do these problems. I am not asking for an answer, I am just asking for someone to point me to a website or question on here that will help…
jimmy
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